Mol Divers (2012) 16:173–181DOI 10.1007/s11030-011-9345-y

FULL-LENGTH PAPER

Synthesis of novel 4H -pyrimido[1,6-a]pyrimidinesvia a one-pot three-component condensation

Jinbao Xiang · Hanghang Li · Kai Yang · Lang Yi ·Yongnan Xu · Qun Dang · Xu Bai

Received: 17 August 2011 / Accepted: 14 November 2011 / Published online: 4 December 2011© Springer Science+Business Media B.V. 2011

Abstract Highly substituted novel 4H -pyrimido[1,6-a]pyrimidines were prepared by a trifluoromethanesulfonicacid catalyzed one-pot three-component condensation of4-aminopyrimidines, aldehydes, and β-ketoesters. A pre-liminaryfeasibilitystudywasundertakenonthesecompounds,to assess the potential production of a library of further diver-sified compounds by nucleophilic replacement of Cl (R1) orby reaction of electrophiles with the NH2 (R2) group.

Keywords MCRs · Multicomponent reactions ·Three-component reaction · 4-Aminopyrimidine ·4H -pyrimido[1,6-a]pyrimidine ·Diversity oriented synthesis · DOS

Introduction

Pyrimidine-fused heterocycles often appear as the core ofbiologically active compounds [1–5] and marketed drugs[6,7]. Consequently, efficient methodologies to access novelscaffolds containing a pyrimidine moiety are of interest inchemical biology and medicinal chemistry [8–12]. Recently,

Electronic supplementary material The online version of thisarticle (doi:10.1007/s11030-011-9345-y) contains supplementarymaterial, which is available to authorized users.

J. Xiang · K. Yang · L. Yi · Q. Dang · X. Bai (B)The Center for Combinatorial Chemistry and Drug Discovery,The School of Pharmaceutical Sciences and The College ofChemistry, Jilin University, 1266 Fujin Road, Changchun,130021 Jilin, People’s Republic of Chinae-mail: xbai@jlu.edu.cn

H. Li · Y. Xu (B)Key Laboratory of Structure-Based Drug Design & Discovery, Ministryof Education, Shenyang Pharmaceutical University, 103 Wenhua Road,Shenyang, 110016 Liaoning, People’s Republic of Chinae-mail: ynxu@syphu.edu.cn

a number of them, e.g., pyrimido[4,5-b][1,6]naphthyri-dine [13], imidazo[5,1-h]pteridine [14], pyrimido[1,6-a]indol-1(2H )-one [15], pyrrolo[2,3-d]pyrimidine [16], werereported. Several pyrimidine-fused structures were also dis-closed by our research laboratory [17–22]. However, thesynthesis of 4H -pyrimido[1,6-a]pyrimidine derivatives hasrarely appeared in literature; even though they offer a uniquering skeleton and multiple substitution patterns, polarity, andhydrogen bonding capabilities. Thus far only one method forthe synthesis of 4H -pyrimido[1,6-a]pyrimidin-4-ones wasreported, which entailed the condensation of 4-aminopy-rimidine with derivatives of Meldrum’s acid [23] or ethylacetoacetate [24].

Multicomponent reations (MCRs) have emerged as a pow-erful tool in the creation of molecular complexity and diver-sity from simple substrates [25]. They have been applied inthe drug discovery process [26] and total synthesis of com-plex natural products [27]. In our ongoing efforts to developmethodologies to access novel pyrimidine-fused heterocy-cles [17–22], we have discovered a versatile one-pot three-component reaction of 4-aminopyrimidines, aldehydes, andβ-ketoesters leading to 4-aryl- or alkyl-substituted 4H -py-rimido[1,6-a]pyrimidines. This class of compounds has highdegree of unsaturation, even though the sp3 carbon at the 4-position makes the [6,6]bicycle not aromatic. Moreover, thechloro and amino functionalities (R1 = Cl, R2 = NH2) inthe products could be further modified to increase their struc-tural diversity. Herein, the results of the studies are reported.

Results and discussion

Initially, the condensation of 6-chloro-4,5-diaminopyrimi-dine 1a and compound 5.1 (prepared from benzaldehyde 2.1and ethyl acetoacetate 3.1 using a published method [28])

123

174 Mol Divers (2012) 16:173–181

Scheme 1 Two-componentcondensation of6-chloro-4,5-diaminopyrimidine1a and compound 5.1

Table 1 Optimization of thetwo-component condensation

All reactions were conductedwith 1.0 mmol of 1a

Bold values indicate the optimalreaction conditions

Entry Acid (equiv) Solvent [1a] (M) 5.1 (equiv) Time (days) 4.1a (yield, %)

1 CF3SO3H (1.0) CH3CN 0.2 1 13 40

2 CF3CO2H (1.0) CH3CN 0.2 1 1 0

3 HCl (1.0) CH3CN 0.2 1 1 0

4 H2SO4 (1.0) CH3CN 0.2 1 1 0

5 CF3SO3H (1.0) CH3CN 2.0 1 3 40

6 CF3SO3H (0.5) CH3CN 2.0 1 3 41

7 CF3SO3H (0.25) CH3CN 2.0 1 3 34

8 CF3SO3H (0.5) CH3CN 2.0 2 3 51

9 CF3SO3H (0.5) CH3CN 2.0 3 3 55

10 CF3SO3H (0.5) 3 3 61

was investigated (Scheme 1). First, the employment of var-ious bases (e.g., DMAP, DBU, K2CO3, Cs2CO3, t-BuOK,and NaH) as promoters of the condensation reaction led toeither the recovery of starting materials or complex reactionmixtures. Next, various acids (e.g., CF3SO3H, CF3CO2H,HCl, and H2SO4) [29] were studied and the results are sum-marized in Table 1. 4H -Pyrimido[1,6-a]pyrimidine 4.1a wassuccessfully obtained in a 40% yield when CF3SO3H wasused after heating for 13 days at 80 ◦C (entry 1), when otheracids failed to give the desired product (entry 2–4). The struc-ture of 4.1a was unambiguously confirmed by X-ray crystal-lographic analysis (Fig. 1). The moderate product yield usingCF3SO3H encouraged us to further optimize the reaction byscreening conditions such as concentration, amount of acid,and ratio of reagents. First, increasing the concentration of 1ato 2.0 M shortened the reaction time to 3 days providing prod-uct with 40% yield (entry 5). Secondly, reducing the amountof CF3SO3H to 0.5 equiv led to 4.1a (entry 6) without sac-rificing yield; further reduction to 0.25 equiv decreased theyield to 34% (entry 7). Thirdly, increasing the ratio of 5.1to 1a increased the yields (entry 8 and 9). Finally, a yield

of 61% was obtained with 0.5 equiv of CF3SO3H, 1 equivof 1a, and 3 equiv of 5.1 after heating for 3 days at 80 ◦C(entry 10).

After achieving a reasonable yield in the two-componentreaction, we speculated that CF3SO3H might also be efficientin promoting the one-pot three-component condensation of4-aminopyrimidine 1a, aldehyde 2.1, and β-ketoester 3.1 toyield 4.1a (Scheme 2). After exploring several reaction con-ditions (Table 2), 4.1a was obtained in 63% yield by heating0.5 equiv CF3SO3H, 1 equiv 1a, 3 equiv 2.1, and 3 equiv 3.1for 21 h at 110 ◦C (entry 3). These conditions were appliedto further studies.

To explore the scope of this one-pot three-componentreaction, several 4-aminopyrimidines 1, aldehydes 2, and β-ketoesters 3 were employed to study the structure activityrelationship under the above optimized reaction conditions(Scheme 3). The results are summarized in Table 3.

As shown in Table 3, 6-chloro-4,5-diaminopyrimidine1a (R1 = Cl, R2 = NH2) reacted with various aldehydes 2(substituted benzaldehydes, heteroaromatic, and aliphaticaldehydes) to produce the desired 4H -pyrimidopyrimidines

123

Mol Divers (2012) 16:173–181 175

Fig. 1 ORTEP diagram of compound 4.1a

4 in moderate yields (entry 1–16). Both electron-donating(entry 2–5)- and electron-withdrawing (entry 6–10)-substi-tuted benzaldehydes were tolerated. The reaction proceededfaster when benzaldehydes with an electron-donating groupwere employed (entry 2–4 vs. entry 6–10). A methyl groupat the ortho benzaldehyde position slowed down the reactioncompared to its corresponding meta- and para-substitutedanalogs (entry 5 vs. entry 3 and 4). Aliphatic aldehydes ledto the desired products (entry 13 and 14) despite the low

yield. Ethyl acetoacetate gave a higher product yield (entry1) compared to ethyl propionylacetate (entry 15) and ethylbenzoylacetate (entry 16). These results indicated that thereaction was sensitive to steric hindrance. Removal of the5-amino group in the aminopyrimidine substrate (1b or 1c,R1 = H or Cl, R2 = H) yielded only trace amounts of prod-uct with molecular ion corresponding to desired product 4.1as detected by LC-MS (entry 17 and 18). However, substitu-tion of the 6-Cl with a secondary amino group in the pyrim-idine ring (R1 = piperidin-1-yl, R2 = H) resulted in a 65%yield of desired product 4.1d (entry 19). To confirm the struc-ture of compound 4.1d X-ray crystallographic analysis wasperformed (Fig. 2). These results implied that a certain levelof electron density in the pyrimidine ring was needed for thedesired reaction to proceed.

The 8-Cl and 9-NH2 moieties of compounds 4a offerattractive sites to introduce different substituents. For thispurpose, compound 4.1a was selected as an example to exam-ine their reactivity toward various nucleophiles and electro-philes as shown in Scheme 4. Compound 4.1a reacted withmorpholine, PhSH, and EtOH to give the desired nucleo-philic substitution products in moderate to high yields. Theamino group reacted with MeI and BnBr under NaH/THFconditions to yield the desired alkylamino products in goodyields. In addition, compounds 8a were obtained in good toexcellent yields in a one-pot process by the reaction of 4.1awith acyl chlorides under mild conditions. These preliminary

Scheme 2 Three-componentreaction of6-chloro-4,5-diaminopyrimidine1a, benzaldehyde 2.1, and ethylacetoacetate 3.1

Table 2 Optimization of thethree-component reaction

All reactions were conductedwith 1.0 mmol of 1a

Bold values indicate the optimalreaction conditions

Entry 2.1 (equiv) 3.1 (equiv) Temp. (◦C) Time (h) 4.1a (yield, %)

1 3 3 80 66 63

2 3 3 100 45 60

3 3 3 110 21 63

4 3 3 120 18 38

5 2 2 110 56 35

6 1 1 110 17 23

Scheme 3 Three-componentreaction of4-aminopyrimidines 1,aldehydes 2, and β-ketoesters 3

123

176 Mol Divers (2012) 16:173–181

Table 3 Preparation of4H -pyrimido[1,6-a]pyrimidines

a The reaction was conducted at60 ◦Cb The reaction was conducted at80 ◦Cc Trace amount with molecularion corresponding to desiredproduct 4.1 was detected byLC-MS

Entry R1 R2 R3 R4 Time (h) Product 4 Yield (%)

1 Cl NH2 Ph Me 21 4.1a 63

2 Cl NH2 p-MeOPh Me 18 4.2a 38

3 Cl NH2 p-MePh Me 20 4.3a 55

4 Cl NH2 m-MePh Me 19 4.4a 46

5 Cl NH2 o-MePh Me 42 4.5a 50

6 Cl NH2 p-ClPh Me 24 4.6a 58

7 Cl NH2 p-BrPh Me 27 4.7a 61

8 Cl NH2 p-FPh Me 23 4.8a 56

9 Cl NH2 p-CNPh Me 44 4.9a 43

10 Cl NH2 p-NO2Ph Me 46 4.10a 53

11 Cl NH2 Thiophen-2-yl Me 62 4.11a 35

12 Cl NH2 Naphthalen-1-yl Me 36 4.12a 44

13 Cl NH2 n-Pr Me 42 4.13a 29a

14 Cl NH2 Cyclopropyl Me 30 4.14a 31b

15 Cl NH2 Ph Et 26 4.15a 40

16 Cl NH2 Ph Ph 28 4.16a 10

17 Cl H Ph Ph 48 4.1b Tracec

18 H H Ph Me 48 4.1c Tracec

19 Piperidin-1-yl H Ph Me 30 4.1d 65

Fig. 2 ORTEP diagram of compound 4.1d

feasibility studies exemplified the potential accessibility of alibrary of structurally diversified compounds through modi-fications of the amino and chloro groups in the heterocycles.

Conclusion

A trifluoromethanesulfonic acid promoted one-pot three-component reaction of 4-aminopyrimidines, aldehydes, andβ-ketoesters was discovered to yield highly substituted novel4H -pyrimido[1,6-a]pyrimidines in moderate to good over-

all yields. The obtained products containing 9-NH2 and 8-Clgroups may undergo electrophilic and/or nucleophilic sub-stitution to yield compounds with further structural diversity.The utility of this reaction has been exemplified by the syn-thesis of few compounds with selected structural features.

Experimental section

General consideration

Acetonitrile (CH3CN) was dried over CaH2 and distilled.Ethanol (EtOH) was distilled from Na and ethyl phthalatebefore usage. Tetrahydrofuran (THF) was dried over P2O5

and distilled from Na before usage. All other commercialreagents were used as received without additional purifica-tion. Melting points were determined using an XT5 melt-ing point apparatus and are uncorrected. Mass spectra andHPLC data was recorded on an 1100 LC/MS system (Agi-lent Technology Corporation) with Alltech ELSD 2000. The1H and 13C NMR data were obtained on a Varian Mercury(300 MHz) NMR spectrometer with TMS as the internal stan-dard and CDCl3 as solvent unless otherwise stated. Multi-plicities are indicated as the following: s, singlet; d, dou-blet; t, triplet; q, quartet; m, multiplet; dd, doubled doublet;

123

Mol Divers (2012) 16:173–181 177

Scheme 4 Derivatizations ofcompounds 4a

br, broad. Coupling constants (J values) where noted arequoted in Hertz.

General procedure for the synthesis of4H-pyrimido[1,6-a]pyrimidine (4)

To a stirred mixture of 4-aminopyrimidine 1 (1 mmol), alde-hyde 2 (3 mmol), and β-ketoester 3 (3 mmol) was addedCF3SO3H (44µL, 0.5 mmol) under N2. The reaction mixturewas stirred for a specified time at 110 ◦C unless otherwisenoted. The reaction mixture was then diluted with CH2Cl2(20 mL), washed with saturated aqueous NaHCO3 or con-centrated ammonia solution (3×5 mL). The combined waterlayers were extracted with CH2Cl2 (3×10 mL). The com-bined organic layers were washed with water (30 mL) andbrine (30 mL) in sequence; dried over Na2SO4 and concen-trated in vacuo. Purification of the resulting residue by flashcolumn chromatography (petroleum ether/EtOAc 8:1–4:1,v/v) afforded the desired product 4.

Ethyl 9-amino-8-chloro-2-methyl-4-phenyl-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.1a)

63%; yellow solid, mp: 130–131 ◦C;1H NMR: δ 7.47 (s, 1H),7.29 (s, 5H), 6.19 (s, 1H), 4.70 (br s, 2H), 4.16–4.10 (m, 2H),2.50 (s, 3H), 1.22 (t, 3H, J = 6.9); 13C NMR (DMSO-d6) : δ

165.1, 155.5, 142.7, 142.2, 136.1, 130.2, 129.0, 128.6, 127.0,126.3, 101.2, 59.5, 58.5, 23.4, 14.1; MS (ESI): m/z 345.1[M + H+].

Ethyl 9-amino-8-chloro-4-(4-methoxyphenyl)-2-methyl-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.2a)

38%; yellow solid, mp: 57–59 ◦C;1H NMR: δ 7.46 (s, 1H),7.21 (d, 2H, J = 7.8), 6.81 (d, 2H, J = 7.2), 6.14 (s, 1H),4.67 (br s, 2H), 4.14–4.11 (m, 2H), 3.76 (s, 3H), 2.50 (s, 3H),1.23 (t, 3H, J = 6.6); 13C NMR (DMSO-d6): δ 165.1, 159.4,155.1, 142.5, 136.1, 134.5, 130.1, 127.8, 127.2, 114.2, 101.4,59.4, 58.0, 55.1, 23.3, 14.1; MS (ESI): m/z 375.1 [M + H+].

Ethyl 9-amino-8-chloro-2-methyl-4-(p-tolyl)-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.3a)

55%; yellow solid, mp: 128–129 ◦C;1H NMR: δ 7.45 (s, 1H),7.17 (d, 2H, J = 8.1), 7.09 (d, 2H, J = 7.8), 6.15 (s, 1H),4.67 (br s, 2H), 4.12 (q, 2H, J = 6.6), 2.49 (s, 3H), 2.29 (s,3H), 1.23 (t, 3H, J = 7.2); 13C NMR (DMSO-d6): δ 165.1,155.3, 142.6, 139.4, 138.1, 136.1, 130.1, 129.4, 126.9, 126.3,101.3, 59.4, 58.3, 23.3, 20.6, 14.1; MS (ESI): m/z 358.9[M + H+].

Ethyl 9-amino-8-chloro-2-methyl-4-(m-tolyl)-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.4a)

46%; yellow solid, mp: 99–100 ◦C;1H NMR: δ 7.46 (s, 1H),7.21–7.08 (m, 4H), 6.15 (s, 1H), 4.69 (br s, 2H), 4.14–4.11(m, 2H), 2.50 (s, 3H), 2.31 (s, 3H), 1.22 (t, 3H, J = 6.9);13C NMR: δ 165.8, 155.5, 142.7, 142.0, 138.7, 136.7, 135.9,129.9, 129.6, 128.8, 127.0, 123.5, 102.0, 60.5, 60.0, 23.5,21.4, 14.2; MS (ESI): m/z 358.9 [M + H+].

123

178 Mol Divers (2012) 16:173–181

Ethyl 9-amino-8-chloro-2-methyl-4-(o-tolyl)-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.5a)

50%; yellow solid, mp: 71–73 ◦C;1H NMR: δ 7.40–7.37 (m,1H),7.33 (s, 1H), 7.17–7.13 (m, 3H), 6.49 (s, 1H), 4.68 (br s,2H), 4.09 (q, 2H, J = 6.9), 2.58 (s, 3H), 2.50 (s, 3H), 1.18(t, 3H, J = 7.2); 13C NMR: δ 165.9, 155.1, 142.6, 141.8,135.8, 133.4, 130.7, 130.1, 128.8, 127.5, 103.0, 60.0, 56.7,23.7, 19.4, 14.3; MS (ESI): m/z 358.9 [M + H+].

Ethyl 9-amino-8-chloro-4-(4-chlorophenyl)-2-methyl-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.6a)

58%; yellow solid, mp: 150–151 ◦C;1H NMR: δ 7.44 (s, 1H),7.30–7.21 (m, 4H), 6.18 (s, 1H), 4.72 (br s, 2H), 4.15–4.11(m, 2H), 2.49 (s, 3H), 1.24 (t, 3H, J = 6.9); 13C NMR(DMSO-d6): δ 165.0, 155.7, 142.6, 141.1, 135.9, 133.3,130.2, 129.0, 128.3, 127.1, 100.9, 59.5, 57.8, 23.4, 14.1; MS(ESI): m/z 378.8 [M + H+].

Ethyl 9-amino-4-(4-bromophenyl)-8-chloro-2-methyl-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.7a)

61%; yellow solid, mp: 160–161 ◦C;1H NMR: δ 7.45–7.42(m, 3H), 7.18–7.15 (m, 2H), 6.16 (s, 1H), 4.70 (br s, 2H),4.16–4.11 (m, 2H), 2.48 (s, 3H), 1.24 (t, 3H, J = 6.9);13C NMR (DMSO-d6): δ 165.0, 155.7, 142.6, 141.5, 135.9,131.9, 130.3, 128.6, 127.1, 122.0, 100.8, 59.6, 57.9, 23.4,14.2; MS (ESI): m/z 422.7 [M + H+].

Ethyl 9-amino-8-chloro-4-(4-fluorophenyl)-2-methyl-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.8a)

56%; yellow solid, mp: 114–115 ◦C;1H NMR: δ 7.45 (s, 1H),7.28 (t, 2H, J = 8.1), 6.99 (t, 2H, J = 8.1), 6.18 (s, 1H),4.71 (br s, 2H), 4.18–4.09 (m, 2H), 2.50 (s, 3H), 1.23 (t,3H, J = 6.9); 13C NMR (DMSO-d6) δ 165.0, 163.6, 160.4,155.5, 142.5, 138.6, 136.0, 130.2, 128.7, 128.6, 127.0, 115.9,115.6, 101.1, 59.5, 57.8, 23.3, 14.1; MS (ESI): m/z 362.9[M + H+].

Ethyl 9-amino-8-chloro-4-(4-cyanophenyl)-2-methyl-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.9a)

43%; yellow solid, mp: 168–169 ◦C;1H NMR: δ 7.62 (d, 2H,J = 8.4), 7.40 (d, 3H, J = 8.4), 6.26 (s, 1H), 4.76 (br s,2H), 4.19–4.12 (m, 2H), 2.48 (s, 3H), 1.25 (t, 3H, J = 6.9);13C NMR (DMSO-d6): δ 164.9, 156.2, 146.8, 142.7, 135.8,133.1, 130.4, 127.3, 127.2, 118.4, 111.5, 100.5, 59.7, 58.0,23.4, 14.2; MS (ESI): m/z 369.9 [M + H+].

Ethyl 9-amino-8-chloro-2-methyl-4-(4-nitrophenyl)-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.10a)

53%; yellow solid, mp: 151–153 ◦C;1H NMR: δ 8.18 (d, 2H,J = 8.7), δ 7.47 (d, 2H, J = 9.0), 7.44 (s, 1H), 6.33 (s, 1H),4.78 (br s, 2H), 4.19–4.13 (m, 2H), 2.49 (s, 3H), 1.26 (t,3H, J = 6.9); 13C NMR (DMSO-d6): δ 164.8, 156.1, 148.5,147.4, 142.7, 135.7, 130.4, 130.3, 127.7, 124.2, 100.4, 59.6,57.8, 23.3, 14.0; MS (ESI): m/z 389.8 [M + H+].

Ethyl 9-amino-8-chloro-2-methyl-4-(thiophen-2-yl)-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.11a)

35%; yellow solid, mp: 115–116 ◦C;1H NMR: δ 7.59 (s, 1H),7.21 (t, 1H, J = 3.3), 6.90 (d, 2H, J = 3.3), 6.49 (s, 1H),4.70 (br s, 2H), 4.23–4.15 (m, 2H), 2.51 (s, 3H), 1.26 (t,3H, J = 7.2); 13C NMR (DMSO-d6): δ 164.9, 155.9, 145.6,142.1, 135.9, 130.2, 127.3, 127.0, 126.8, 125.2, 101.4, 59.6,53.6, 23.3, 14.2; MS (ESI): m/z 350.8 [M + H+].

Ethyl 9-amino-8-chloro-2-methyl-4-(naphthalen-1-yl)-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.12a)

44%; yellow solid, mp: 149–150 ◦C;1H NMR: δ 8.43 (d,1H, J = 8.4), 7.87 (d, 1H, J = 8.1), 7.81 (d, 1H, J = 8.1),7.68–7.62 (m, 2H), 7.53 (t, 1H, J = 7.5), 7.47–7.40 (m,2H), 7.14 (s, 1H), 4.72 (br s, 2H), 3.99–3.90 (m, 2H), 2.57 (s,3H), 0.95 (t, 3H, J = 6.9); 13C NMR (DMSO-d6): δ 165.0,154.5, 142.2, 139.9, 135.3, 133.2, 130.4, 129.3, 128.9, 128.6,127.1, 126.7, 126.5, 126.0, 125.9, 123.1, 102.8, 59.2, 54.0,23.2, 13.8; MS (ESI): m/z 394.9 [M + H+].

Ethyl 9-amino-8-chloro-2-methyl-4-propyl-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.13a)

29%; oil; 1H NMR: δ 7.38 (s, 1H), 5.11 (s, 1H), 4.63 (brs, 2H), 4.25–4.21 (m, 2H), 2.41 (s, 3H), 1.35–1.14 (m, 7H),0.88 (t, 3H, J = 7.2); 13C NMR(DMSO-d6):δ 165.1, 155.8,143.0, 135.9, 129.8, 127.2, 100.7, 59.2, 55.4, 38.4, 23.1, 17.3,14.2, 13.4; MS (ESI): m/z 311.0 [M + H+].

Ethyl 9-amino-8-chloro-4-cyclopropyl-2-methyl-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.14a)

31%; yellow solid, mp: 96–97 ◦C;1H NMR: δ 7.42 (s, 1H),4.67 (br s, 3H), 4.26–4.20 (m, 2H), 2.44 (s, 3H), 1.33 (t, 3H,J = 6.6), 1.21 (s, 1H); 0.59–0.46 (m, 3H), 0.28 (s, 1H);13C NMR: δ 166.3, 156.6, 142.9, 135.4, 129.6, 128.6, 100.3,60.3, 60.0, 23.5, 18.2, 14.4, 3.66, 3.56; MS (ESI): m/z 308.9[M + H+].

123

Mol Divers (2012) 16:173–181 179

Ethyl 9-amino-8-chloro-2-ethyl-4-phenyl-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.15a)

40%; yellow solid, mp: 116–118 ◦C;1H NMR: δ 7.47 (s, 1H),7.30 (s, 5H), 6.18 (s, 1H), 4.70 (br s, 2H), 4.16–4.10 (m, 2H),2.92–2.88 (s, 2H), 1.22 (t, 6H, J = 6.9); 13C NMR: δ 165.5,160.7, 142.9, 141.7, 135.8, 130.0, 129.0, 128.8, 128.3, 126.4,101.3, 90.3, 60.4, 60.0, 29.1, 14.1, 12.8; MS (ESI): m/z 359.1[M + H+].

Ethyl 9-amino-8-chloro-2,4-diphenyl-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.16a)

10%; yellow solid, mp: 162–163 ◦C;1H NMR: δ 7.54 (s, 1H),7.45–7.29 (m, 10H), 6.32 (s, 1H), 4.75 (br s, 2H), 3.94–3.87(m, 2H), 0.87 (t, 3H, J = 6.9); 13C NMR (DMSO-d6): δ

165.4, 155.4, 142.6, 141.7, 140.1, 135.9, 130.6, 129.0, 128.8,128.7, 128.3, 127.3, 126.2, 100.1, 59.3, 58.7, 13.5; MS (ESI):m/z 407.1 [M + H+].

Ethyl 2-methyl-4-phenyl-8-(piperidin-1-yl)-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (4.1d)

65%; yellow solid, mp: 154–156 ◦C;1H NMR: δ 7.78 (s, 1H),7.32–7.21 (m, 5H), 6.02 (s, 1H), 5.82 (s, 1H), 4.13–4.05 (m,2H); 3.54 (s, 4H), 2.47 (s, 3H), 1.65–1.56 (m, 6H), 1.22 (t,3H, J = 6.6); 13C NMR: δ 166.3, 158.8, 158.6, 151.9, 148.4,143.5, 128.7, 128.1, 126.3, 97.7, 87.8, 59.9, 59.2, 45.7, 25.3,24.24, 24.17, 14.3; MS (ESI): m/z 379.2 [M + H+].

Preparation of ethyl 9-amino-2-methyl-8-morpholino-4-phenyl-4H- pyrimido[1,6-a]pyrimidine-3-carboxylate(6.1a)

To a stirred solution of compound 4.1a (173 mg, 0.5 mmol)in n-BuOH (4 mL) was added morpholine (0.45 mL, 5 mmol)followed by Et3N (1.66 mL, 12 mmol). The resulting solutionwas stirred for 8 h at reflux. The volatiles were removed invacuo, water (10 mL) was added and the reaction mixture wasextracted with EtOAc (2×10 mL). The combined organiclayers were washed with brine (10 mL), dried (Na2SO4), andconcentrated in vacuo. Purification of the resulting residueby flash column chromatography (petroleum ether/EtOAc8:1–4:1, v/v) afforded 170 mg (86%) of 6.1a as a yellowsolid. mp: 163–164 ◦C;1H NMR: δ 7.60 (s, 1H), 7.29 (s,5H), 6.20 (s, 1H), 4.11 (br s, 4H), 3.79 (s, 4H), 3.34–3.14(m, 4H), 2.52 (s, 3H), 1.22 (t, 3H, J = 6.3); 13C NMR: δ

166.2, 157.2, 145.4, 142.9, 137.1, 130.9, 128.8, 128.4, 126.4,120.5, 98.8, 66.9, 60.8, 59.5, 47.4, 24.1, 14.3; MS (ESI): m/z395.9 [M + H+].

Preparation of ethyl 9-amino-2-methyl-4-phenyl-8-(phenylthio)-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate(6.2a)

To a stirred solution of compound 4.1a (173 mg, 0.5 mmol)in EtOH (3 mL) was added PhSH (0.51 mL, 5 mmol) fol-lowed by Et3N (1.66 mL, 12 mmol). The resulting solutionwas stirred for 4 h at reflux. The volatiles were removed invacuo, water (10 mL) was added and the reaction mixture wasextracted with CH2Cl2 (3×10 mL). The combined organiclayers were washed with brine (10 mL), dried (Na2SO4), andconcentrated in vacuo. Purification of the resulting residueby flash column chromatography (petroleum ether/EtOAc8:1–4:1, v/v) afforded 178 mg (85%) of 6.2a as a yellowsolid. mp: 119–120 ◦C;1H NMR: δ 7.52 (s, 1H), 7.35–7.24(m, 10H), 6.16 (s, 1H), 4.90 (br s, 2H), 4.15–4.10 (m, 2H),2.50 (s, 3H), 1.22 (t, 3H, J = 7.2); 13C NMR: δ 166.0, 156.1,142.5, 136.5, 134.2, 130.8, 129.3, 129.0, 128.8, 127.6, 126.6,102.2, 60.5, 60.0, 23.8, 14.4; MS (ESI): m/z 418.9 [M + H+].

Preparation of ethyl 9-amino-8-ethoxy-2-methyl-4-phenyl-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (6.3a)

To a stirred solution of Na (230 mg, 10 mmol) in absoluteEtOH (8 mL) was added compound 4.1a (344 mg, 1 mmol) at0 ◦C under N2. The resulting solution was stirred for 1 h at re-flux. Saturated aqueous NH4Cl was added to quench the reac-tion. The volatiles were removed in vacuo, water (10 mL) wasadded and the reaction mixture was extracted with CH2Cl2(3×10 mL). The combined organic layers were washed withbrine (10 mL), dried (Na2SO4), and concentrated in vacuo.Purification of the resulting residue by flash column chroma-tography (petroleum ether/EtOAc 6:1, v/v) afforded 160 mg(45%) of 6.3a as a yellow solid. mp: 102–103 ◦C.1H NMR: δ7.56 (s, 1H), 7.29–7.25 (m, 5H), 6.25 (s, 1H), 4.39–4.34 (m,2H), 4.16–4.08 (m, 4H), 2.51 (s, 3H), 1.37 (t, 3H, J = 6.9),1.23 (t, 3H, J = 6.9); 13C NMR: δ 166.4, 157.6, 149.6,143.1, 136.3, 128.8, 128.3, 126.3, 116.9, 97.8, 63.0, 60.9,59.5, 24.4, 14.8, 14.4; MS (ESI): m/z 354.9 [M + H+].

General procedure for the synthesis of compound (7a)

To a stirred solution of compound 4.1a (344 mg, 1 mmol)in THF (5 mL) was added NaH (75 mg, 2.5 mmol, 80% dis-persion in oil) at 0 ◦C under N2. After 30 min, a solution ofMeI or BnBr (3 mmol) in THF (2 mL) was added dropwise.The reaction mixture was stirred for a specified time at roomtemperature. Saturated aqueous NH4Cl was added to quenchthe reaction. The volatiles were removed in vacuo, water(10 mL) was added and the reaction mixture was extractedwith EtOAc (3×10 mL). The combined organic layers werewashed with brine (10 mL), dried (Na2SO4), and concen-trated in vacuo. Purification of the resulting residue by flash

123

180 Mol Divers (2012) 16:173–181

column chromatography (petroleum ether/EtOAc 20:1, v/v)afforded the desired product 7.1a or 7.2a.

Ethyl 8-chloro-2-methyl-9-(methylamino)-4-phenyl-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (7.1a)

Yellow solid, 77%, mp: 91–92 ◦C;1H NMR: δ 7.41 (s, 1H),7.28–7.26 (m, 5H), 6.15 (s, 1H), 5.52 (br d, 1H, J = 4.2),4.16–4.08 (m, 2H), 3.20 (d, 3H, J = 5.4), 2.48 (s, 3H), 1.22(t, 3H, J = 6.9); 13C NMR (DMSO-d6): δ 165.0, 154.9,144.1, 142.0, 136.4, 131.4, 128.9, 128.6, 126.8, 126.3, 101.7,59.5, 58.4, 31.9, 23.2, 14.1; MS (ESI): m/z 359.1 [M + H+].

Ethyl 9-(benzylamino)-8-chloro-2-methyl-4-phenyl-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate (7.2a)

Yellow solid, 62%, mp: 96–97 ◦C;1H NMR: δ 7.43 (s, 1H),7.32–7.18 (m, 10H), 6.14 (s, 1H), 5.84 (t, 1H, J = 7.2), 4.77(dd, 2H, J = 7.2, 2.7), 4.17–4.09 (m, 2H); 2.47 (s, 3H), 1.23(t, 3H, J = 7.2); 13C NMR: δ 165.7, 155.2, 144.8, 139.5,136.2, 130.7, 129.9, 128.9, 128.7, 128.5, 127.2, 126.2, 102.4,60.3, 48.5, 29.6, 23.5, 14.2; MS (ESI): m/z 435.0 [M + H+].

General procedure for the synthesis of compound (8a)

To a stirred solution of compound 4.1a (344 mg, 1 mmol)in dimethylacetamide (5 mL) was added CH3COCl or Ph-COCl (5 mmol). The reaction mixture was stirred for a spec-ified time at 60 ◦C, water (10 mL) was added, and extractedwith CH2Cl2 (3×10 mL). The combined organic layers werewashed with brine (10 mL), dried (Na2SO4), and concen-trated in vacuo. Purification of the resulting residue by flashcolumn chromatography (petroleum ether/EtOAc 2:1, v/v)afforded the desired product 8.1a or 8.2a.

Ethyl 2,9-dimethyl-7-phenyl-7H-oxazolo[4,5-e]pyrimido[1,2-c]pyrimidine-8-carboxylate (8.1a)

Yellow solid, 84%, mp: 201–202 ◦C;1H NMR: δ 7.91 (s, 1H),7.38–7.28 (m, 5H), 6.28 (s, 1H), 4.20–4.10 (m, 2H), 2.61 (s,3H), 2.58 (s, 3H); 1.24 (t, 3H, J = 7.2); 13C NMR: δ 165.7,160.0, 146.8, 143.8, 142.0, 129.0, 128.9, 126.3, 121.3, 103.1,60.7, 60.1, 23.5, 14.4, 14.1; MS (ESI): m/z 351.1 [M + H+].

Ethyl 9-methyl-2,7-diphenyl-7H-oxazolo[4,5-e]pyrimido[1,2-c]pyrimidine-8-carboxylate (8.2a)

Yellow solid, 93%, mp: 214–215 ◦C;1H NMR: δ 8.24 (dd,2H, J = 7.8, 1.5), 7.98 (s, 1H), 7.55–7.47 (m, 3H), 7.41–7.28(m, 5H), 6.32 (s, 1H), 4.22–4.11 (m, 2H); 2.64 (s, 3H), 1.25 (t,3H, J = 6.9); 13C NMR: δ 165.6, 161.7, 159.9, 155.0, 147.1,143.9, 141.9, 129.1, 129.0, 128.8, 127.4, 126.4, 125.6, 122.5,103.4, 60.8, 60.1, 23.5, 14.1; MS (ESI): m/z 413.0 [M + H+].

Acknowledgments The authors are very grateful to Professor Yaz-hong Pei for his helpful discussions and inputs in preparation of themanuscript. This work was supported by National Natural ScienceFoundation of China (No. 20902036), National Science & TechnologyMajor Project “Key New Drug Creation and Manufacturing Program”of China (No. 2009ZX09501-010) and Changchun Discovery Sciences,Ltd.

References

1. Horton DA, Bourne GT, Smythe ML (2003) The combinatorialsynthesis of bicyclic privileged structures or privileged substruc-tures. Chem Rev 103:893–930. doi:10.1021/cr020033s

2. Gangjee A, Lin X, Queener SF (2004) Design, synthesis, and bio-logical evaluation of 2,4-diamino-5-methyl-6-substituted-pyrrol-o[2,3-d]pyrimidines as dihydrofolate reductase inhibitors. J MedChem 47:3689–3692. doi:10.1021/jm0306327

3. Curtin NJ, Barlow HC, Bowman KJ, Calvert AH, Davison R,Golding BT, Huang B, Loughlin PJ, Newell DR, Smith PG,Griffin RJ (2004) Resistance-modifying agents. 11. Pyrimido[5,4-d]pyrimidine modulators of antitumor drug activity. Synthesis andstructure-activity relationships for nucleoside transport inhibitionand binding to α1-acid glycoprotein. J Med Chem 47:4905–4922.doi:10.1021/jm040772w

4. Cossrow J, Guan B, Ishchenko A, Jones JH, Kumaravel G, Lu-govskoy A, Peng H, Powell N, Raimundo BC, Tanaka H, VesselsJ, Wynn T, Xin Z (2009) Heterocyclic compounds useful as RAFkinase inhibitors. Patent US20090005359

5. Dehnhardt CM, Venkatesan AM, Santos ED, Chen Z, Santos O,Ayral-Kaloustian S, Brooijmans N, Mallon R, Hollander I, Feld-berg L, Lucas J, Chaudhary I, Yu K, Gibbons J, Abraham R,Mansour TS (2010) Lead optimization of N-3-substituted 7-morpholinotriazolopyrimidines as dual phosphoinositide 3-kinase/mammalian target of rapamycin inhibitors: discovery ofPKI-402. J Med Chem 53:798–810. doi:10.1021/jm9014982

6. Kompis IM, Islam K, Then RL (2005) DNA and RNA synthesis:antifolates. Chem Rev 105:593–620. doi:10.1021/cr0301144

7. Bikker JA, Brooijmans N, Wissner A, Mansour TS (2009) Kinasedomain mutations in cancer: implications for small moleculedrug design strategies. J Med Chem 52:1493–1509. doi:10.1021/jm8010542

8. Nefzi A, Ostresh JM, Houghten RA (1997) The current statusof heterocyclic combinatorial libraries. Chem Rev 97:449–472.doi:10.1021/cr960010b

9. Dolle RE, Le Bourdonnec B, Goodman AJ, Morales GA, SalvinoJM, Zhang W (2007) Comprehensive survey of chemical librariesfor drug discovery and chemical biology: 2006. J Comb Chem9:855–902. doi:10.1021/cc700111e

10. Dolle RE, Le Bourdonnec B, Goodman AJ, Morales GA, ThomasCJ, Zhang W (2008) Comprehensive survey of chemical librariesfor drug discovery and chemical biology: 2007. J Comb Chem10:753–802. doi:10.1021/cc800119z

11. Dolle RE, Le Bourdonnec B, Goodman AJ, Morales GA, ThomasCJ, Zhang W (2009) Comprehensive survey of chemical librariesfor drug discovery and chemical biology: 2008. J Comb Chem11:739–790. doi:10.1021/cc9000828

12. Dolle RE, Le Bourdonnec B, Worm K, Morales GA, Thomas CJ,Zhang W (2010) Comprehensive survey of chemical libraries fordrug discovery and chemical biology: 2009. J Comb Chem 12:765–806. doi:10.1021/cc100128w

13. Han Z, Zhang G, Jiang B, Ma N, Shi F, Tu S (2009) Diversitysynthesis of pyrimido[4,5-b][1,6]naphthyridine and its derivativesunder microwave irradiation. J Comb Chem 11:809–812. doi:10.1021/cc800196u

123

Mol Divers (2012) 16:173–181 181

14. Sharma S, Kundu B (2009) Application of the modified Pic-tet-Spengler cyclization reaction for the preparation of animidazopyrazine ring: Synthesis of new pyrido- and pyrimi-do-imidazopyrazines. J Comb Chem 11:720–731. doi:10.1021/cc9000345

15. Wang Z, Yang J, Yang F, Bao W (2010) One-pot synthesis ofpyrimido[1,6-a]indol-1(2H)-one derivatives by a nucleophilicaddition/Cu-catalyzed N-arylation/Pd-catalyzed C-H activationsequential process. Org Lett 12:3034–3037. doi:10.1021/ol101041e

16. EI Kaïm L, Grimaud L, Wagschal S (2010) Toward pyrrolo[2,3-d]pyrimidine scaffolds. J Org Chem 75:5343–5346. doi:10.1021/jo100759b

17. Fu R, Xu X, Dang Q, Chen F, Bai X (2007) Rapid access to pyrim-ido[5,4-c]isoquinolines via a sulfur monoxide extrusion reaction.Org Lett 9:571–574. doi:10.1021/ol0627146

18. Xiang J, Zheng L, Chen F, Dang Q, Bai X (2007) A cascadereaction consisting of Pictet-Spengler-type cyclization and Smilesrearrangement: Application to the synthesis of novel pyrrole-fuseddihydropteridines. Org Lett 9:765–767. doi:10.1021/ol0629364

19. Che X, Zheng L, Dang Q, Bai X (2008) Synthesis of novel pyrim-idine fused 8-membered heterocycles via iminium ion cyclizationreactions. J Org Chem 73:1147–1149. doi:10.1021/jo7020746

20. Zheng L, Yang F, Dang Q, Bai X (2008) A cascade reaction withiminium ion isomerization as the key step leading to tetrahydro-pyrimido[4,5-d]pyrimidines. Org Lett 10:889–892. doi:10.1021/ol703049j

21. Xu G, Zhang L, Wang S, Dang Q, Bai X (2009) Regiospec-ific syntheses of 3-aza-alpha-carbolines via inverse electron-demand Diels-Alder reactions of 2-aminoindoles with 1,3,5-tri-azines. Synlett 3206–3210. doi:10.1055/s-0029-1218345

22. Xiang J, Wen D, Xie H, Dang Q, Bai X (2010) Synthesis ofnovel 8,9-dihydro-5H -pyrimido[4,5-e][1,4]diazepin-7(6H)-ones.J Comb Chem 12:503–509. doi:10.1021/cc100039w

23. Dennin F, Blondeau D, Sliwa H (1990) Synthesis of 9-hydrox-ypyrimido[1,6-a]pyrimidin-4-one and its derivatives. J HeterocyclChem 27:1963–1967. doi:10.1002/jhet.5570270721

24. Vasudevan A, Mavandadi F, Chen L, Gangjee A (1999) Reac-tions of 6-aminopyrimidines with biselectrophiles: Manipulationof product composition with solvent and pyrimidine substitutionvariation. J Org Chem 64:634–638. doi:10.1021/jo9713870

25. Dömling A (2006) Recent developments in isocyanide based mul-ticomponent reactions in applied chemistry. Chem Rev 106:17–89.doi:10.1021/cr0505728

26. Armstrong RW, Combs AP, Tempest PA, Brown SD, KeatingTA (1996) Multiple-component condensation strategies for com-binatorial library synthesis. Acc Chem Res 29:123–131. doi:10.1021/ar9502083

27. Touré BB, Hall DG (2009) Natural product synthesis using multi-component reaction strategies. Chem Rev 109:4439–4486. doi:10.1021/cr800296p

28. Antonioletti R, Bovicelli P, Malancona S (2002) A new route to2-alkenyl-1,3-dicarbonyl compounds, intermediates in the syn-thesis of dihydrofurans. Tetrahedron 58:589–596. doi:10.1016/S0040-4020(01)01173-5

29. Wabnitz TC, Spencer JB (2003) A general, Brønsted acid-cata-lyzed hetero-Michael addition of nitrogen, oxygen, and sulfurnucleophiles. Org Lett 5:2141–2144. doi:10.1021/ol034596h

123