A facile new procedure for the deprotection of allyl ethers under mild conditions

A facile new procedure for the deprotection ofallyl ethers under mild conditions

Yun-Jin Hu, Romyr Dominique, Sanjoy Kumar Das, and René Roy

Abstract: A novel isomerization ofO-allyl glycosides into prop-1-enyl glycosides was observed instead ofcross-metathesis during an olefin metathesis reaction using Grubbs’ ruthenium benzylidene catalyst(Cy3P)2RuCl2=CHPh (1), N-allyltritylamine, andN,N-diisopropylethylamine as necessary auxiliary reagents. In thesearch for a better catalytic system, it has been found that dichlorotris(triphenylphosphine)ruthenium(II),[(C6H5)3P]3RuCl2, (2) was much more efficient for the isomerization of allylic ethers. The labile prop-1-enyl group waseasily hydrolyzed using HgCl2–HgO and the hemiacetals (25–32) were isolated in excellent yields (ca. 90%).

Key words: allyl ether, carbohydrate, Grubbs’ catalyst, isomerization, metathesis, deprotection.

Résumé: Au cours d’une réaction de métathèse d’oléfine impliquant du catalyseur de Grubbs, le benzylidène deruthénium, (Cy3P)2RuCl2=CHPh (1), de laN-allyltritylamine et duN,N-diisopropyléthylamine comme réactifsauxiliaires nécessaires, on a observé une nouvelle isomérisation des glycosides deO-allyle en glycosides deprop-2-ényle. Au cours de nos travaux en vue développer un meilleur système catalytique, on a trouvé que ledichlorotris(triphénylphosphine)ruthénium(II), [(C6H5)3P]3RuCl2 (2), est beaucoup plus efficace pour l’isomérisation deséthers allyliques. Le groupe prop-1-ényle labile est hydrolysé facilement à l’aide de HgCl2–H2O et on a isolé leshémiacétals (25–32) avec d’excellents rendements (environ 90%).

Mots clés: éther allylique, catalyseur de Grubbs, isomérisation, métathèse, déprotection.

[Traduit par la Rédaction] Hu et al. 845

Introduction

The use of allyl ether protecting groups is of great impor-tance in carbohydrate chemistry and other natural productsyntheses (1) because of their ready availability and stabilityunder reasonably strong acidic and basic conditions. Severalmethods for the deprotection of allyl ethers have alreadybeen described in the literature (2–11). Most methods in-volve initial isomerization of allyl to prop-1-enyl ethers witheither a base such as [(CH3)3COK] (2) or transition metals:Ti(0) (3), Rh(I) (4), Ir(I) (5), Pd-C (6), Pd(PPh3)4 (7),Pd(OAc)2 (7), H2Ru(PPh3)4 (8), Fe(CO)5 (9). The labileprop-1-enyl ethers can then be cleaved to the correspondingalcohols by mineral acids or HgCl2–HgO (10) (Scheme 1).Direct cleavage of allyl ethers is generally carried out usingstoichiometric amounts of palladium salts or complexes suchas PdCl2(PhCN)2, PdCl2 (11). However, some of these meth-ods are still less than satisfactory for practical use and some-times are found to be capricious (12). Herein, we wish toreport a new method for the deprotection of the allyl groupfrom carbohydrate derivatives using Grubbs’ ruthenium

benzylidene catalyst (Cy3P)2RuCl2=CHPh 1 or dichloro-tris(triphenylphosphine)ruthenium(II) (2) in excellent yields(ca. 90%).

Results and discussion

Recently we have been interested in the metathesis reac-tion of O-allyl glycosides using Grubbs’ catalyst(Cy3P)2Cl2Ru=CHPh (1) (13, 14). However, when thecross-metathesis reaction betweenN-allyltritylamine 3 (15)and allyl 2,3,4,6-tetra-O-acetyl-α-D-galactopyranoside9 (16)was carried out with1, an unexpected isomerization product17 was isolated in 30% yield instead of the anticipated crossmetathesis compound. Furthermore, neither sugar norN-allyltritylamine dimer could be detected. Treatment of9with 1,4-diazabicyclo[2,2,2]octane (DABCO) in the presenceof Grubbs’ catalyst1 afforded only 4% of the isomerizedproduct17 together with 40% of allylα-D-galactopyranosidehomodimer (14). Similar results were obtained whentriethylamine was used as base. Neither isomerization normetathesis products were detected when diethylamine orpyridine were used (Table 1, entries 6 and 7). The isomer-ized product17 was obtained with the highest yield when9was treated with diisopropylethylamine (DIPEA) in the pres-ence of Grubbs’ catalyst1. However, all the isomerizationyields of those reactions were still very low in the absenceof N-allyltritylamine 3 (Scheme 2). When both3 and 1equiv. of DIPEA were simultaneously used in the reaction,the isomerization yield was improved dramatically to 80%(Table 1, entry 8). Furthermore, there was no self-metathesisproduct that could be detected.

Can. J. Chem.78: 838–845 (2000) © 2000 NRC Canada

838

Received November 8, 1999. Accepted April 4, 2000.Published on the NRC Research Press website on June 13,2000.

Y.-J. Hu, R. Dominique, S.K. Das, and R. Roy.1

Department of Chemistry, University of Ottawa, Ottawa, ONK1N 6N5, Canada.

1Author to whom correspondence may be addressed.Telephone: (613) 562-5800, ext 6055. Fax: (613) 562-5170.e-mail: [email protected]

I:\cjc\cjc78\cjc-06\V00-073.vpThursday, June 08, 2000 10:26:35 AM

Color profile: DisabledComposite Default screen

Bearing in mind the above observations, alternative baseswhich could provide both basicity and olefinic functionalitywere explored. To this end, severalN-allylated amine deriva-tives (4–8) that could mimic the structure of amine3 weresynthesized to test the reaction. It was found that Boc-allylcarbamate4 and amine5 did not catalyze this reaction at all.Several tertiary amines6–8 with increasing chain length alsofailed to afford the desired isomerization products with3and catalyst1 when they were subjected to the optimumconditions. This demonstrates that the strong steric hin-drance ofN-allyltritylamine also had an important influenceon the isomerization of9 as well as its basicity. At thisstage, we believed the presence of the secondary amine3 asan auxiliary reagent was crucial for the isomerization tooccur.

More detailed studies showed that the isomerization ofallyl ethers to propenyl ethers with Grubbs’ catalyst pro-ceeded smoothly in the presence of amine3 and a stoichio-metric amount of base such as diisopropylethylamine(DIPEA). To improve the yield of the isomerization and sup-press the formation of metathesis products, 1.0 equiv. ofDIPEA and 2.0 equiv. of3 were treated with different glyco-sides in the presence of 0.1 equiv. of1 (toluene, reflux, 4 h).Good yields were obtained without any metathesis productbeing detected in any of these experiments (Table 2).

The ratios of the unseparatedE andZ stereoisomers in thepro-1-enyl glycosides were determined from the analysis ofthe 1H NMR spectra of the crude mixtures by observation ofthe 3JH,H coupling constants of the alkenyl protons (17). In-terestingly, thecis stereoisomers predominated. Isomeriza-tion of partially protected glycosides12 and15 proceeded inlower yields, presumably because some of the remainingfree hydroxyl groups of the substrates coordinated to someextent with the catalyst and reduced or prevented its activity.When control experiments were performed in the absence of3 and DIPEA, only the expected self-metathesis productswere obtained in high yields (14).

We noticed that olefin isomerization of allylic etherand allyl alcohol can be catalyzed by Ru(II)(H2O)6(tos)2(tos = p-toluenesulfonate) (18) in aqueous solution and

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Hu et al. 839

Entry Base or additiveRecycledglycosides (%)

Self metathesissugar dimer (%) Isomerization (%)

1 3 67 — 302 DABCO 55 40 43 Et3N 45 45 34 NMMa 80 12 65 DIPEA 35 50 106 Diethylamine 100 — —7 Pyridine 100 — —8 3 and DIPEA 16 — 809 4 78 20 —

10 5 65 30 —aNMM: N-methylmorpholine.

Table 1. Isomerization of allylα-D-galactopyranoside9 with different bases or additives in the presence ofGrubbs’ catalyst (1).

Scheme 1.

Scheme 2.



(PPh3)2X2Ru=CH-CH=CPh2 (X = Cl or CF3COO) (19) indichloromethane. When compared to existing methodologies,however, Ru(II)(H2O)6(tos)2, (PPh3)2X2Ru=CH-CH=CPh2, orGrubbs’ catalyst are relatively expensive and the isomeri-zation yields are not competitive. We therefore initiated asearch for a better catalyst by screening a family of ruthe-nium complexes for activity in this reaction. From this in-

vestigation, it was found that the commercially available,dichlorotris(triphenylphosphine)ruthenium(II) [(PPh3)3RuCl2(2)] can be used as an efficient catalyst for the deprotectionof allyl group from the glycosides9–16 following a two-stepprocedure.

We began with the isomerization reaction of peracetylatedallyl α-D-galactopyranoside (9) in different aprotic solvents

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840 Can. J. Chem. Vol. 78, 2000

Table 2. Results from the isomerization and hemiacetal transformations (25–32) (HgCl2–HgO) of various allyl glycosides (9–16) intoprop-1-enyl glycosides (17–24) in the presence of Grubbs’ catalyst1 and amine3, or catalyst2 (Ph3P)3Cl2Ru(II) and DIPEA (PhCH3,reflux, 4 h).



such as tetrahydrofuran, acetonitrile, dichloromethane, andtoluene in the presence of2 and DIPEA (Table 3). Noisomerization was detected when THF and acetonitrile wereused as solvents. When the reaction was carried out inrefluxing dichloromethane, the isomerized product (17) wasobtained in 80% yield. The best result was obtained whenthe reaction was performed in toluene under refluxing condi-tions. Lower yields were obtained when the reactions wereperformed in anhydrous methanol or aqueous ethanol due tocompeting de-O-acetylation. It is noteworthy that no iso-merized product was detected in the absence of catalyst orbase, even under forcing conditions such as prolonged reac-tion time, higher reaction temperature, and the use of up to20 mol% of catalyst. Several common organic bases wereexamined for activity in the isomerization of11. Noisomerization product was formed in pyridine. Upon treat-ment with triethylamine or 1,4-diazabicyclo[2,2,2]octane,the isomerization reactions proceeded smoothly. It was foundthat diisopropylethylamine (DIPEA) was the most suitablebase for the system in terms of the high yields obtained forboth 9 and 11 (Table 3). This novel isomerization reactionmost likely follows the metal hydride addition-eliminationmechanism (18).

Various allyl glycosides were subjected to the followingstandard conditions: a catalytic amount of2 (10 mol%) wasutilized as catalyst and a stoichiometric amount of DIPEA asbase and the reactions were performed in refluxing toluene.Isomerized products were obtained in excellent yields (Ta-ble 2). It is also noteworthy that even thoseO-allyl gly-

cosides (12, 15) with free hydroxyl groups, which were notsuitable for the metathesis reaction because of the coordina-tion to the metal in the Grubbs’ catalyst, were still good sub-strates for these isomerization conditions.

As expected, hydrolysis of the enol ethers proceeded rap-idly under acidic conditions (pH = 2) to provide hemiacetals(4). Alternatively, treatment of prop-1-enyl ethers withHgCl2–HgO in aqueous acetone at room temperature for 1 hgave deprotected products in high yields. The whole proce-dure could be simplified as a two-step one-pot reaction: afterisomerization of allyl ether, toluene and DIPEA were re-moved under reduced pressure and the resulting residue wasthen subjected to 0.5 equiv. of HgO and 1.0 equiv. of HgCl2in aqueous acetone (water:acetone – v/v 1:1) at room tem-perature for 1 h.

The excellent results described above provide a new routetowards the deprotection ofO-allyl glycosides in the field ofcarbohydrate chemistry. Up to now, there were several meth-ods reported for the deprotection ofO-allyl ethers (2–10,20–22), however, these methods have been limited by severereaction conditions such as: using strong base (2) or strongacid (20) as catalyst, performing reactions in aqueous alco-hol (4) or alkaline solution (9), using oxidizing (21) or re-ducing (22) conditions, and operating under severeoxygen-free and anhydrous conditions (5). Compared toWilkinson’s catalyst (4), which is commonly used fordeprotection ofO-allyl ether in carbohydrate chemistry, ru-thenium (II) complexes have two advantages with similarlyeffective performancewith respect to promoting the

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Hu et al. 841

Scheme 3.

Entry Glycoside Base Solvent Time (h) Product Yield (%)

1 9 DIPEA THF 2 17 02 9 DIPEA CH3CN 2 17 03 9 DIPEA CH2Cl2 2 17 804 9 DIPEA Toluene 1 17 965 9 DIPEA Ethanol:H2O (9:1) 2 17 -a

6 9 DIPEA Methanol 2 17 -a

7 9 — Toluene 6 17 08 11 Pyridine Toluene 6 19 09 11 NMOb Toluene 6 19 54

10 11 DABCOc Toluene 2 19 8511 11 Et3N Toluene 3 19 8212 11 DIPEA Toluene 2 19 94

aDeacetylation was detected during the isomerization.bNMO: N-methylmorpholine oxide.c1,4-Diazabicyclo[2.2.2]octane.

Table 3. [(Ph3P)3RuCl2]-catalyzed isomerization ofO-allyl glycosides (9, 11).



isomerization ofO-allyl glycosides. First, the ruthenium(II) complex is more than two times cheaper thanWilkinson’s catalyst; second, the ruthenium (II) complexdoes not reduce the alkene as is sometimes observed whenusing (Ph3P)3RhCl (23). As for Felkin’s Ir (I) catalyst, whichis not commercially available, the procedure must be per-formed under strictly oxygen-free and anhydrous conditions(5). Our method for the isomerization of allyl groups bydichlorotris(triphenylphosphine)ruthenium(II) (2) is widelyapplicable and easy to perform under mild reaction condi-tions (Table 2). The isomerization ofO-allyl ethers proceedsreadily at refluxing temperature without affecting freehydroxyl, O-isopropylidene, trityl, acetyl, benzyl, orp-methoxylbenzyl groups.

Saloman and coworkers (24) reported the selective rear-rangement ofdiallyl ethers catalyzed by dichlorotris(triphenyl-phosphine)ruthenium(II) (2) involving a preliminaryrearrangement to allyl vinyl ethers followed by a Claisen re-arrangement. However, high temperature (200°C) instead ofan organic base was used in their experiments. A recent re-port showed that isomerization ofO-allyl ethers using2 at130°C led to the formation of many byproducts (9), so itwould appear that its use has not been exploited until now.To the best of our knowledge, there are no other reports ofthe application of this catalyst for the deprotection ofO-allylgroups.

The simplicity and mildness of this methodology led us toexplore this procedure for the deprotection of allyl etherfrom 6-O-allyl-1,2:3,4-di-O-isopropylidene-α-D-galactopy-ranose (33). Treatment of33 with catalyst2 and DIPEA un-der the same reaction conditions gave the isomerizedproduct34 in 95% yield (Scheme 3).

Conclusions

In conclusion, an efficient isomerization ofO-allyl glyco-sides has been achieved in the presence of a catalyticamount of dichlorotris(triphenylphosphine)ruthenium(II) (2),from which we have developed a facile method for thedeprotection of O-allyl acetals and ethers. This ispreparatively a very useful method, which is performedunder mild conditions and is compatible with the presenceof various protecting groups. It is also worth noting that thecommercially available polystyrene-anchored (PPh3)2RuCl2should show similar activity towards the isomerization ofO-allyl glycosides, which would make the actual procedureeven more attractive (25).

Experimental section

Materials1H and 13C NMR spectra were recorded at 500 or

200 MHz and 125 or 50 MHz respectively, with tetramethyl-silane (0.00 ppm) as an internal reference. Thin-layer chro-matography (TLC) was performed using silica gel 60 F254aluminum sheets purchased from E. Merck. Reagents usedfor developing plates include ceric sulfate (1% w/v) and am-monium sulfate (2.5% w/v) in 10% (v/v) aqueous sulfuricacid, iodine, dilute aqueous potassium permanganate, andUV light. TLC plates were heated to approximately 150°Cwhen necessary. Purifications were performed by gravity or

flash chromatography on silica gel 60 (230–400 mesh; E.Merck No. 9385). Solvents were evaporated under reducedpressure using a rotary evaporator connected to a water aspi-rator. All chemicals used in experiments were of reagentgrade. Solvents were purified by published procedures.Compounds10 and11 were synthesized by the reported pro-cedure(26). Compound12 was prepared by the methodreported by Fraser–Reid et al. (27). Allylα-L-rhamnopy-ranosides (13–15) were prepared according to the method re-ported by Luckas et al. (28). Allyl glycoside16 wassynthesized by the published procedure (16).

Typical procedure for isomerization of glycosides byGrubbs’ catalyst (1); procedure A

To a solution of glycoside (0.1 mmol) in toluene (2 mL),N-allyltritylamine (3) (0.2 mmol), Grubbs’ catalyst1(8.2 mg, 0.01 mmol) and DIPEA (0.1 mmol) were added un-der a nitrogen atmosphere. The reaction mixture was stirredunder reflux conditions for 4 h. The resulting red solutionwas concentrated using a rotary evaporator and the residuewas partitioned between water and dichloromethane. The or-ganic layer was dried (Na2SO4), concentrated, and purifiedby column chromatography.

Typical procedure for isomerization using (Ph3P)3Cl2Ru(2); procedure B

To a solution of glycosides (0.1 mmol) in toluene (2 mL),dichlorotris(triphenylphosphine)ruthenium(II) (9.6 mg,0.01 mmol) and DIPEA (0.2 mmol) were added under a ni-trogen atmosphere. The resulting solution was stirred underreflux conditions for 2 h and then toluene and DIPEA wereremoved under reduced pressure. The residue was purifiedby silica gel column chromatography to obtain the appropri-ate isomerized product.

Procedure for the deprotection of prop-1-enyl groupThe purified isomerization product (0.1 mmol) was dis-

solved in 2 mL of acetone:water (1:1). To the solution, HgO(10.8 mg, 0.05 mmol) and HgCl2 (27.2 mg, 0.1 mmol) wereadded. After stirring for 1 h atroom temperature, with moni-toring by TLC, the deprotected product was extracted withethyl acetate and washed with potassium iodide solution toremove mercuric compounds. Following a usual work-up,colorless oil was obtained and purified by silica gel columnchromatography to obtain the appropriate product as anαandβ mixture.

Prop-1-enyl 2,3,4,6-tetra-O-acetyl-α-D-galactopyranoside (17):After silica gel column chromatography with ethyl acetateand hexane as eluent (1:2), compound17 (as a mixture ofEandZ isomers in 1:2 ratio) was isolated as a syrup,Rf (hex-ane:EtOAc = 2:1): 0.38. ForE isomer:1H NMR (200 MHz,CDCl3), δ : 6.13 (dq, 1H,J = 12.3, 1.6 Hz), 5.50–5.35 (m,2H), 5.36–5.29 (m, 1H), 5.25–5.09 (m, 2H), 4.27–4.15 (m,1H), 4.12–3.98 (m, 2H), 2.14 (s, 3H), 2.07 (s, 3H), 2.02 (s,3H), 2.00 (s, 3H), 1.55 (dd, 3H,J = 7.0, 1.6 Hz). ForZ iso-mer: 1H NMR (200 MHz, CDCl3), δ : 6.05 (dq, 1H,J = 6.1,1.6 Hz), 5.50–5.35 (m, 2H), 5.36–5.29 (m, 1H), 5.25–5.09(m, 1H), 4.70–4.59 (m, 1H), 4.27–4.15 (m, 1H), 4.12–3.98(m, 2H), 2.14 (s, 3H), 2.07 (s, 3H), 2.02 (s, 3H), 2.00 (s,

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3H), 1.62 (dd, 3H,J = 6.9, 1.6 Hz). HRMS(FAB), calcd. forC17H24O10K (M + K +): 427.1007, found: 427.1456.

Prop-1-enyl 2-acetamido-3,4-di-O-acetyl-2-deoxy-6-O-trityl-β-D-glucopyranoside (18): Compound18 (as a Z isomer)was obtained from10 as a syrup in 85% yield using Grubbs’catalyst. The expected product was obtained in 95% yieldusing catalyst2. Rf (hexane:EtOAc = 1:1): 0.23. ForZ iso-mer: 1H NMR (200 MHz, CDCl3), δ (ppm): 7.60–7.00 (m,15H), 6.29 (dq, 1H,J = 6.2, 1.7 Hz), 5.54 (d, 1H,J =9.2 Hz), 5.26–5.23 (m, 2H), 4.83 (d, 1H,J = 8.2 Hz),4.75–4.68 (m, 1H), 4.20–4.15 (m, 1H), 3.61–3.52 (m, 1H),3.31–3.12 (m, 2H), 2.07 (s, 3H), 2.02 (s, 3H), 1.78 (s, 3H),1.68–1.65 (m, 3H). HRMS (FAB), calcd. for C34H37N1O8K(M + K+): 626.2156, found: 626.2150.

Prop-1-enyl 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-β-D-glucopy-ranoside (19): Known compound19 (29) (E:Z = 1:3) wasobtained as a colorless oil in 70% yield using Grubbs’ cata-lyst and 92% yield using catalyst2. Rf (hexane:EtOAc =1:6): 0.34. ForE isomer: 1H NMR (500 MHz, CDCl3), δ(ppm): 6.19 (m, 1H), 5.62 (d, 1H,J = 8.8 Hz), 5.31 (dd, 1H,J = 10.2, 9.2 Hz), 5.15–5.05 (m, 2H), 4.83 (d, 1H,J =8.3 Hz), 4.26 (dd, 1H,J = 12.2, 4.5 Hz), 4.13 (dd, 1H,J =10.0, 2.3 Hz), 4.03 (m, 1H), 3.78 (m, 1H), 2.08 (s, 3H), 2.04(s, 3H), 2.02 (s, 3H), 1.95 (s, 3H), 1.55 (dd, 3H,J = 6.8,1.7 Hz). For Z isomer: 1H NMR (500 MHz, CDCl3), δ(ppm): 6.15 (dq, 1H,J = 4.5, 1.7 Hz), 5.62 (d, 1H,J =8.8 Hz), 5.31 (dd, 1H,J = 10.2, 9.2 Hz), 5.10 (m, 1H), 4.83(d, 1H, J = 8.3 Hz), 4.61 (m, 1H), 4.26 (dd, 1H,J = 12.2,4.5 Hz), 4.13 (dd, 1H,J = 10.0, 2.3 Hz), 4.03 (m, 1H), 3.78(m, 1H), 2.08 (s, 3H), 2.04 (s, 3H), 2.02 (s, 3H), 1.95 (s,3H), 1.56 (dd, 3H,J = 6.9, 1.7 Hz).13C NMR (125 MHz,CDCl3), δ (ppm): 170.5, 170.4, 170.3, 142.4 (E), 141.2 (Z),105.7 (E), 105.6 (Z), 95.9 (E), 95.3 (Z), 67.9, 67.7, 67.5,66.8, 61.4, 20.6, 12.3 (E), 9.2 (Z). HRMS (FAB), calcd. forC17H26NO9 (M + 1): 388.1608, found: 388.1877.

Prop-1-enyl 3,4-O-isopropylidene-β-D-galactopyranoside (20):Compound20 (E:Z = 1:1) was obtained as colorless oil in20% yield using Grubbs’ catalyst. The expected product20was obtained in 92% yield using catalyst2. Rf (hex-ane:EtOAc = 1:3): 0.32. ForE isomer:1H NMR (200 MHz,CDCl3), δ (ppm): 6.24 (dq, 1H,J = 12.3, 1.7 Hz), 5.23–5.10(m, 1H), 4.41 (d, 1H,J = 8.3 Hz), 4.30–4.07 (m, 2H),4.06–3.58 (m, 4H), 2.38 (d, 1H,J = 2.4 Hz), 1.62–1.36 (m,9H). For Z isomer: 1H NMR (200 MHz, CDCl3), δ (ppm):6.17 (dq, 1H,J = 6.4, 1.6 Hz), 5.23–5.10 (m, 1H), 4.70–4.57(m, 1H), 4.41 (d, 1H,J = 8.3 Hz), 4.30–4.07 (m, 2H),4.06–3.58 (m, 4H), 2.38 (d, 1H,J = 2.4 Hz), 1.62–1.36 (m,9H). 13C NMR (50 MHz, CDCl3), δ (ppm): 143.6 (E), 142.6(Z), 110.5, 105.0 (E), 104.5 (Z), 101.9 (Z), 101.3 (E), 78.7,73.8, 73.7, 73.1, 62.2, 28.0, 26.2, 12.2 (E), 9.4 (Z). MS(FAB) m/z: 260 (M+).

Prop-1-enyl2,3-di-O-benzyl-4-O-(p-methoxybenzyl)-α-L-rhamnopy-ranoside (21): Compound21 (E:Z = 1:1) was isolated from13 as a syrup in 77% and 94% yield using Grubbs’ catalyst(1) and catalyst2, respectively.Rf (hexane:EtOAc = 10:1):0.40. ForE isomer:1H NMR (500 MHz, CDCl3), δ (ppm):7.40–6.86 (m, 14H), 6.12 (dq, 1H,J = 12.4, 1.6 Hz),5.05–4.95 (m, 1H), 4.96 (d, 1H,J = 1.0 Hz), 4.89–4.56 (m,

6H), 3.91–3.59 (m, 4H), 3.80 (s, 3H), 1.53–1.51 (m, 3H),1.32 (d, 3H,J = 5.7 Hz). For Z isomer:1H NMR (500 MHz,CDCl3), δ (ppm): 7.40–6.86 (m, 14H), 6.10 (dq, 1H,J = 6.9,1.6 Hz), 4.96 (d, 1H,J = 1.0 Hz), 4.89–4.56 (m, 6H),4.55–4.46 (m, 1H), 3.91–3.59 (m, 4H), 3.80 (s, 3H),1.53–1.51 (m, 3H), 1.32 (d, 3H,J = 5.7 Hz). MS (FAB) m/z:504 (M+).

Prop-1-enyl 2,3,4-tri-O-acetyl-α-L-rhamnopyranoside (22):Compound (E:Z = 1:2) was obtained as a syrup in 95% yieldusing procedure B,Rf (hexane:EtOAc = 1:4): 0.27. ForEisomer:1H NMR (200 MHz, CDCl3), δ (ppm): 6.13 (dq, 1H,J = 12.3, 1.7 Hz), 5.40–5.00 (m, 4H), 4.94 (s, 1H), 3.84 (dq,1H, J = 9.7, 6.2 Hz), 2.15 (s, 3H), 2.05 (s, 3H), 1.99 (s, 3H),1.55 (dd, 3H,J = 7.0, 1.7 Hz), 1.21 (d, 3H,J = 6.2 Hz). ForZ isomer: 1H NMR (200 MHz, CDCl3), δ (ppm): 6.07 (dq,1H, J = 6.2, 1.7 Hz), 5.40–5.00 (m, 3H), 4.94 (s, 1H),4.73–4.55 (m, 1H), 3.84 (dq, 1H,J = 9.7, 6.2 Hz), 2.15 (s,3H), 2.05 (s, 3H), 1.99 (s, 3H), 1.63 (dd, 3H,J = 7.0,1.7 Hz), 1.21 (d, 3H,J = 6.2 Hz).13C NMR (50 MHz,CDCl3), δ (ppm): 169.9, 169.9, 169.8, 141.6 (E), 140.7 (Z),105.3 (E), 105.0 (Z), 97.1 (Z), 96.5 (E), 70.9, 70.8, 69.2,68.8, 66.8, 20.9, 17.4, 12.4 (E), 9.3 (Z). HRMS (FAB),calcd. for C15H23O8 (M + 1): 331.1733, found: 331.1749.

Prop-1-enyl 4-O-(p-methoxybenzyl)-α-L-rhamnopyranoside (23):Compound23 (E:Z = 1:2) was obtained from15 as colorlessoil in 96% yield using catalyst2. For E isomer:1H NMR(500 MHz, CDCl3), δ (ppm): 7.28 (d, 2H,J = 7.7 Hz), 6.87(d, 2H,J = 7.7 Hz), 6.16 (dq, 1H,J = 12.2, 1.6 Hz), 5.03 (m,1H), 4.96 (d, 1H,J = 1.5 Hz), 4.65–4.48 (m, 2H), 3.98–3.63(m, 3H), 3.75 (s, 3H), 3.32 (dq, 1H,J = 9.4, 4.4 Hz), 2.57(bs, 1H), 1.54–1.50 (m, 3H), 1.32 (d, 3H,J = 4.4 Hz). ForZisomer: 7.28 (d, 2H,J = 7.7 Hz), 6.87 (d, 2H,J = 7.7 Hz),6.08 (dq, 1H,J = 6.1, 1.9 Hz), 4.96 (d, 1H,J = 1.5 Hz),4.65–4.48 (m, 3H), 3.98–3.63 (m, 3H), 3.75 (s, 3H), 3.32(dq, 1H,J = 9.4, 4.4 Hz), 2.37 (bs, 1H), 1.54–1.50 (m, 3H),1.32 (d, 3H,J = 4.4 Hz). 13C NMR (125 MHz, CDCl3), δ(ppm): 142.4 (E), 141.3 (Z), 129.7, 114.1, 104.5 (E), 103.8(Z), 99.0 (Z), 98.5 (E), 81.0, 74.7, 71.3, 70.4, 67.9, 55.3,17.9, 12.4 (E), 9.2 (Z). HRMS (FAB), calcd. for C17H24O6(M + 1): 324.1573, found: 324.1708.

Prop-1-enyl 2,3,4,6-tetra-O-benzyl-α-D-mannopyranoside (24):Compound24 (E:Z = 1:1) was obtained as colorless syrup in84%, Rf (hexane:EtOAc = 4:1): 0.30,E:Z = 1:1. ForE iso-mer: 1H NMR (500 MHz, CDCl3), δ (ppm): 7.46–7.24 (m,20H), 6.25 (dq, 1H,J = 12.3, 1.6 Hz), 5.18 (br, 1H), 5.16(m, 1H), 4.98–4.58 (m, 8H), 4.16 (t, 1H,J = 8.6 Hz), 4.06(dd, 1H,J = 8.6, 1.0 Hz), 3.95–3.78 (m, 4H), 1.61 (m, 3H).For Z isomer: 1H NMR (500 MHz, CDCl3), δ (ppm):7.46–7.24 (m, 20H), 6.21 (dq, 1H,J = 6.7, 1.6 Hz), 5.18 (br,1H), 4.98–4.58 (m, 8H), 4.60 (m, 1H), 4.16 (t, 1H,J =8.6 Hz), 4.06 (dd, 1H,J = 8.6, 1.0 Hz), 3.95–3.78 (m, 4H),1.61 (m, 3H).13C NMR (125 MHz, CDCl3), δ (ppm): 142.5(E), 141.5 (Z), 138.5, 128.4, 128.3, 128.1, 128.0, 127.8,127.7, 127.6, 127.5, 104.6 (E), 103.8 (Z), 98.0 (Z), 97.8 (E),80.1, 75.3, 75.1, 74.7, 73.4, 73.3, 72.4, 72.3, 69.0, 12.5 (E),9.3 (Z). HRMS (FAB), calcd. for C37H40O6K (M + K +):619.2462, found: 619.2437.

© 2000 NRC Canada

Hu et al. 843



2,3,4,6-Tetra-O-acetyl-α,β-D-galactopyranose (25) (30): Thepurified isomerized product17 (38.8 mg, 0.1 mmol) was dis-solved in 2 mL of acetone:water (1:1), then HgO (10.8 mg,0.05 mmol) and HgCl2 (27.2 mg, 0.1 mmol) were added.The reaction mixture was stirred for 20 min at roomtemperature, monitored by TLC, the deprotected productwas extracted with ethyl acetate and washed with potassiumiodide solution to remove mercuric compounds. Following ausual work-up, known compound25 (30) was obtained in92% yield,α:β = 3:1. Forα anomer:1H NMR (500 MHz,CDCl3), δ (ppm): 5.47 (dd, 1H,J = 3.4, 3.3 Hz), 5.43 (m,1H), 5.37 (dd, 1H,J = 10.9, 3.3 Hz), 5.11 (dd, 1H,J = 10.7,3.4 Hz), 4.43 (t, 1H,J = 6.7 Hz), 4.06 (m, 1H), 4.05 (m,1H), 3.68 (bs, 1H), 2.11 (s, 3H), 2.05 (s, 3H), 2.01 (s, 3H),1.95 (s, 3H). Forβ anomer:1H NMR (500 MHz, CDCl3), δ(ppm): 5.43 (m, 1H), 5.37 (dd, 1H,J = 10.9, 3.3 Hz), 5.04(m, 1H), 4.67 (dd, 1H,J = 7.8, 7.4 Hz), 4.11 (d, 1H,.J =7.4 Hz), 4.06 (m, 1H), 4.05 (m, 1H), 3.93 (t, 1H,J =6.7 Hz), 2.11 (s, 3H), 2.05 (s, 3H), 2.01 (s, 3H), 1.95 (s,3H). 13C NMR (125 MHz, CDCl3), δ (ppm): 171.0, 170.6,170.5, 170.4, 170.2, 170.1, 170.0, 95.9, 90.6, 71.0, 70.4,68.3, 68.2, 67.2, 66.1, 61.8, 61.5, 42.4, 20.6. MS (FAB)m/z:349 (M + 1).

2-Acetamido-3,4-di-O-acetyl-2-deoxy-6-O-trityl- α,β-D-gluco-pyranose (26): Compound26 (as anα andβ mixture) wasobtained from18 in 92% yield as colorless oil,Rf (hex-ane:EtOAc = 1:1): 0.20. Forα anomer:1H NMR (200 MHz,CDCl3), δ (ppm): 7.33 (m, 15H), 5.79 (d, 1H,J = 9.3 Hz),5.30–5.18 (m, 3H), 4.33–4.12 (m, 2H), 3.55 (d, 1H,J =2.5Hz), 3.20 (dd, 1H,J = 10.4, 2.1 Hz), 3.04 (dd, 1H,J =10.4, 4.6 Hz), 1.98 (s, 3H), 1.91 (s, 3H), 1.70 (s, 3H). Forβanomer:1H NMR (200 MHz, CDCl3), δ (ppm): 7.33 (m,15H), 5.79 (d, 1H, J = 9.3 Hz), 5.30–5.18 (m, 2H),4.33–4.12 (m, 3H), 4.12 (m, 1H), 3.55 (d, 1H,J = 2.5Hz),3.20 (dd, 1H,J = 10.4, 2.1 Hz), 3.04 (dd, 1H,J = 10.4,4.6 Hz), 1.98 (s, 3H), 1.91 (s, 3H), 1.70 (s, 3H). MS(FAB) m/z: 471 (M + 1).

3,4-O-Isopropylidene-α,β-D-galactopyranose (28): Com-pound28 (α:β = 2:1) was obtained as a syrup in 90% yieldfrom 20, Rf (EtOAc): 0.23. For α anomer: 1H NMR(500 MHz, CDCl3), δ (ppm): 5.61 (bs, 1H), 5.23 (bs, 1H),4.30–3.5 (m, 6H), 1.49 (s, 3H), 1.30 (s, 3H). Forβ anomer:1H NMR (500 MHz, CDCl3), δ (ppm): 6.32 (bs, 1H), 4.65(bs, 1H), 4.30–3.5 (m, 6H), 1.49 (s, 3H), 1.30 (s, 3H).13CNMR (125 MHz, CDCl3), δ (ppm): 110.4 (β ), 109.8 (α),95.9 (β isomer), 91.3 (α), 79.1, 75.6, 74.3, 74.1, 73.8, 73.4,69.2, 68.9, 62.5, 62.2, 28.0, 27.4, 26.3, 25.7. HRMS (FAB),calcd. for C9H17O6 (M + 1): 221.1025, found: 221.1289.

2,3-Di-O-benzyl-4-O-(p-methoxybenzyl)-α,β-L-rhamnopyranose(29): Compound29 (α:β = 5:1) was obtained as syrup in91% yield,Rf (hexane:EtOAc = 4:1): 0.25. Forα anomer:1HNMR (500 MHz, CD3COCD3), δ (ppm): 7.43–7.24 (m,12H), 6.86 (d, 2H,J = 8.6 Hz), 5.17 (s, 1H), 4.84–4.57 (m,6H), 3.89 (m, 2H), 3.82 (m, 1H), 3.77 (s, 3H), 3.52 (t, 1H,J= 9.1 Hz), 1.18 (d, 3H,J = 6.2 Hz). Forβ anomer:1H NMR(500 MHz, CD3COCD3), δ (ppm): 7.43–7.24 (m, 12H), 6.86(d, 2H, J = 8.6 Hz), 4.84–4.57 (m, 7H), 3.89 (m, 2H), 3.82(m, 1H), 3.77 (s, 3H), 3.52 (t, 1H,J = 9.1 Hz), 1.18 (d, 3H,J = 6.2 Hz). 13C NMR (125 MHz, CD3COCD3), δ (ppm):

140.2, 132.2, 130.4, 129.1, 129.0, 128.9, 128.7, 128.5,128.4, 128.2, 128.1, 114.3, 93.0 (β ), 92.9 (α), 83.9, 81.2,77.2, 75.4, 73.3, 72.4, 68.2, 55.5, 18. HRMS (FAB), calcd.for C28H33O6 (M + 1): 465.2277, found: 465.2224.

2,3,4-Tri-O-acetyl-α,β-L-rhamnopyranose (30): Knowncompound30 (31) was obtained from22 as a syrup in 92%yield, α:β = 13:1. For α anomer: 1H NMR (500 MHz,CD3COCD3), δ (ppm): 6.02 (d, 1H,J = 4.4 Hz), 5.29 (dd,1H, J = 10.1, 3.5 Hz), 5.17 (dd, 1H,J = 3.5, 1.8 Hz), 5.09(dd, 1H,J = 4.4, 1.8 Hz), 4.99 (t, 1H,J = 10.1 Hz), 4.05 (m,1H), 2.07 (s, 3H), 2.01 (s, 3H), 1.95 (s, 3H), 1.91 (s, 3H),1.12 (d, 3H,J = 6.3 Hz).13C NMR (125 MHz, CD3COCD3),δ (ppm): 170.5, 170.4, 170.3, 92.6, 71.7, 71.4, 69.8, 66.6,20.7, 17.9. HRMS (FAB), cacld. for C12H19O8 (M + 1):291.0180, found: 291.0216.

4-O-(p-Methoxybenzyl)-α,β-L-rhamnopyranose (31): Com-pound31 (α:β = 9:1) was obtained as colorless oil in 93%.For α anomer:1H NMR (500 MHz, CD3COCD3), δ (ppm):7.29 (d, 2H,J = 8.7 Hz), 6.87 (d, 2H,J = 8.7 Hz), 5.31 (d,1H, J = 4.0 Hz), 5.05 (bs, 1H), 4.83 (d, 1H,J = 10.9 Hz),4.58 (d, 1H,J = 11.0 Hz), 4.00–3.80 (m, 3H), 3.76 (s, 3H),3.32 (dd, 1H,J = 9.3, 9.0 Hz), 1.16 (d, 3H,J = 6.3 Hz). Forβ anomer:1H NMR (500 MHz, CD3COCD3), δ (ppm): 7.29(d, 2H, J = 8.7 Hz), 6.87 (d, 2H,J = 8.7 Hz), 5.16 (d, 1H,J= 9.3 Hz), 4.68 (d, 1H,J = 9.3 Hz), 4.83 (d, 1H,J =10.9 Hz), 4.58 (d, 1H,J = 11.0 Hz), 4.00–3.80 (m, 3H), 3.76(s, 3H), 3.32 (dd, 1H,J = 9.3, 9.0 Hz), 1.19 (d, 3H,J =5.8 Hz).13C NMR (125 MHz, CD3COCD3), δ (ppm): 160.0,132.4, 130.3, 114.3, 95.0, 82.2, 74.8, 73.2, 72.4, 67.6, 55.5,14.5. HRMS (FAB), calcd. for C14H20O6K (M + K +):323.0897, found: 323.1397.

2,3,4,6-Tetra-O-benzyl-α,β-D-mannopyranose (32): Com-pound32 (α:β = 3:1) was obtained as colorless oil in 78%yield, Rf (hexane:EtOAc = 4:1): 0.20. Forα anomer: 1HNMR (500 MHz, CDCl3), δ (ppm): 7.60–7.00 (m, 20H),5.25 (d, 1H,J = 1.6Hz), 5.05–4.49 (m, 8H), 4.04 (m, 1H),3.96 (dd, 1H,J = 9.6, 2.8 Hz), 3.86 (t, 1H,J = 9.6 Hz), 3.79(dd, 1H,J = 2.8, 1.6 Hz), 3.73–3.67 (m, 2H). Forβ anomer:1H NMR (500 MHz, CDCl3), δ (ppm): 7.60–7.00 (m, 20H),5.05–4.49 (m, 9H), 4.04 (m, 1H), 3.96 (dd, 1H,J = 9.6,2.8 Hz), 3.86 (t, 1H,J = 9.6 Hz), 3.79 (dd, 1H,J = 2.8,1.6 Hz), 3.73–3.67 (m, 2H).13C NMR (125 MHz, CDCl3), δ(ppm): 138.4, 138.4, 138.3, 138.0, 128.5, 128.5, 128.3,128.3, 128.1, 128.0, 127.9, 127.9, 127.8, 127.8, 127.7,127.6, 127.6, 127.5, 127.5, 93.7 (β isomer), 92.7 (α isomer),79.7, 74.6, 73.3, 72.7, 72.6, 72.2, 71.5, 69.6. MS (FAB)m/z:541 (M + 1).

1,2:3,4-Di-O-isopropylidene-6-O-(prop-1-enyl)-α-D-galactopyr-anose (34): Compound34 was obtained from33 (32) in95% yield as a syrup,Rf (hexane:EtOAc = 1:6): 0.40.E:Z =5:1. For E-isomer, 1H NMR (500 MHz, CDCl3), δ (ppm):6.20 (dq, 1H,J = 12.6, 1.6 Hz), 5.50 (d, 1H,J = 5.0 Hz),4.77 (m, 1H), 4.57 (dd, 1H,J = 7.9, 2.5 Hz), 4.28 (dd, 1H,J= 5.0, 2.5 Hz), 4.22 (dd, 1H,J = 7.9, 2.0 Hz), 3.99 (m, 1H),3.80 (dd, 1H,J = 10.3, 5.9 Hz), 3.74 (dd, 1H,J = 10.3,6.8 Hz), 1.54 (dd, 3H,J = 6.8, 1.7 Hz), 1.41 (s, 3H), 1.30 (s,3H), 1.29 (s, 6H).13C NMR (125 MHz, CDCl3), δ (ppm):146.2, 109.3, 108.6, 98.9, 96.3, 70.6, 70.5, 67.4, 66.1, 25.9,

© 2000 NRC Canada

844 Can. J. Chem. Vol. 78, 2000



© 2000 NRC Canada

Hu et al. 845

24.9, 24.4, 12.4. HRMS (FAB), calcd. for C15H25O6 (M + 1):301.1691, found: 301.1624.

1,2:3,4-Di-O-isopropylidene-α-D-galactopyranose (35):Known compound352 was obtained from34 in 91% yield ascolorless oil, Rf (hexane:EtOAc = 1:3): 0.30.1H NMR(200 MHz, CDCl3), δ (ppm): 5.55 (d, 1H,J = 5.0 Hz), 4.60(dd, 1H, J = 7.9, 2.2 Hz), 4.32 (dd, 1H,J = 5.0, 2.2 Hz),4.25 (dd, 1H,J = 7.9, 1.2 Hz), 3.86–3.80 (m, 4H), 1.51 (s,3H), 1.44 (s, 3H), 1.32 (s, 6H).

Acknowledgements

Support of this work by the Natural Sciences and Engi-neering Research Council of Canada (NSERC) is gratefullyacknowledged.

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2The spectral data of35 were identical with the product from Aldrich Chemical Co.



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A facile new procedure for the deprotection of allyl ethers under mild conditions