Organic Reactions in Crystals

Organic Reactions in Crystals

Fumio Toda

Department of Applied Chemistry, Faculty of Engineering, Ehime University,

Abstract: By utilizing the phenomenon that molecules move from crystal to crystal

quite easily under appropriate conditions, a new type of organic chemistry has

beencontrived.. The combination of the enantioselective molecular movement from

racemic guest crystal to chiral host crystal with fractional distillation, leads to a

process whereby enantiomeric guest molecules can be separated by distillation. Selective and efficient organic reactions can be carried out by grinding crystals of

substrate and reagent.

1. Introduction

Since molecules are arranged tightly and regularly in crystals, chemical reactions in this

environment are expected to proceed efficiently and selectively. However, in most cases,

molecules in crystalline media are not arranged at appropriate positions for reactions to occur.

In order to control the arrangement of molecules in a crystal, host molecules are introduced.

By accommodation of guest molecules in the crystalline lattice formed by host molecules, the

guest molecules are arranged in the appropriate position for the solid state reaction. When

stereoselective reactions are desired, assistance by the host compound is in most cases

imperative. In particular, enantioselective reactions are easily facilitated by use of the

appropriate chiral host compounds. For this reason, most reactions in the solid state are

usually carried out in the host-guest inclusion crystal. The question remains as to what kind of

host compounds are necessary?. Thus in this paper we wish to report on the design of various

kinds of host compounds based on a simple but unique principle.

The host-guest inclusion complex crystal is usually prepared by recrystallization of the two

components from a particular solvent of choice. During the course of the study of inclusion

crystallization, however, we found that the complexation occurs in the solid state. By mixing

powdered host and guest crystals, inclusion complexation occurred not only efficiently but also enantioselectively. Finally, we established a new distillatory resolution method by the

combination of enantioselective solid state complexation and fractional distillation. By using

this method, various racemic guest compounds were resolved efficiently in the presence of

Vol.52, No.11 (November 1994) ( 51 ) 923

chiral host compounds.

The easy molecular movement of molecules from crystal to crystal prompted us to carry out

a solid-solid reaction between substrate crystal and reagent crystal. Indeed certain solid state

reactions proceeded efficiently and selectively. In general, we observed that an inclusion

crystal of substrate and chiral host was reacted with a reagent in the solid state, an

enantioselcetive reaction occurred.

2. Design of Host Compounds.

As early as 1968, we found that 1,1,6,6-tetraphenyl-2,4-hexadiyne-1,6-diol (1a) and

1,1,4,4-tetrapheny1-2-butyne-1,4-diol (1 b) included various kinds of guest compounds in

stoichiometric ratios and formed inclusion complex crystals (ref.1). Since recrystallization of

la and lb rendered inclusion of almost all solvents used, it was very difficult to prepare pure crystals of la and lb themselves. Spectral and X-ray structure analytical data showed that the

solvent guest molecules are included by forming hydrogen bonds with the hydroxyl group of

the host. The solventless crystals of la and lb were finally obtained by recrystallization from

non-polar solvents such as hexane. These results suggested an idea for the design of new host

compounds. The acetylenic linkage is not essential, because 1,1,2,2-tetraphenylethane-1,2-

diol (1 c) also shows similar inclusion ability (ref. 2). The extremely high inclusion ability of

these hosts is probably due to the sterically crowded hydroxyl groups. Due to this steric restriction, la and lb, respectively can not associate intermolecularly through the formation of

hydrogen bonds and so a guest molecule is accommodated as depicted schematically in Fig. 1,

forming the hydrogen bond network Host-OH---Guest---HO-Host.. Alcohols which have

sterically bulky substituents should therefore be good host compounds. Along these lines

various hosts including chiral ones were designed. Of the chiral hosts, (S,S)-(+1,6-di(o-chloropheny1)-1,6-dipheny1-2,4-hexadiyne-1,6-diol (2) (ref. 3), (R,R)-(-)-4,5-bis(hydroxy-

diphenylmethyl)-2,2-dimethyl- 1,3-dioxacyclopentane (3a) and its derivatives (3b, 3c) (ref.4)

were found to be promising candidates.

1

23

Fig. 1. Alcohol host substituted with bulky groups

924 ( 52 ) J. Synth. Org. Chem., Jpn.

3. Host-Guest Inclusion Crystallization

As indicated earlier host-guest inclusion complexations are usually carried out by

recrystallization of together both the host and guest compounds from solvent. The criteria for

choice of solvent, is any solvent which shows a lower affinity towards the host compound

relative to that of the guest molecule. In some cases, however, solvent molecules are included

together with the guest molecule. In these cases, solvent molecules necessarily occupy a

vacant space of and stabilize the host-guest inclusion crystalline lattice. In special cases, the

solvent molecule which is included along with the guest molecule plays an important and

interesting role in molecular recognition. For example, recrystallization of 4a and rac- 5 from

toluene and MeOH gave a 1:2 complex of 4a and (+)-5 and a 1:1:1 complex of 4a, (-)-5 and

MeOH, respectively (ref. 5). Similarly, recrystallization of 4 b and rac-6 from toluene and

MeOH gave a 1:1 complex of 4 b and (-)-6 and a 1:1:1 complex of 4 b, (+)-6 and MeOH, respectively (ref. 5). In the absence and presence of MeOH, the chiral hosts 4a and 4 b

recognize the different enantiomer of 5 and 6, respectively.

(S,S)-(-)- 45 6

7

a : Ar =

b: Ar = 89 10

1112

Inclusion complexation can also be achieved by mixing powdered host and guest

compounds (ref. 6). For example, when a mixture of powdered la and chalcone (7) was kept at room temperature for 6 h, a 1:2 inclusion complex of la and 7 was formed. The

complexation can be followed by measurement of an UV spectrum in the solid state. As the

complexation proceeded, molecules of 7 having a coplanar structure increased which was

followed by an increase in absorption. It is to noted that the coplanar structure of 7 in the

inclusion complex had already been established from earlier work (ref. 7).

Surprisingly, it was also discovered that the solid state complexation occurs enantioselectively. A mixture of finely powdered 3c and rac-8 was kept at room temperature for 1 day and then washed with hexane to give a complex of 3c and (+)-8 and hexane solution.

Vol.52, No.11 (November 1994)

( 53 ) 925

From the complex, (+)-8 of 88% ee was obtained in 24% yield by distillation in vacuo. From

the hexane solution, (-)-8 of 36% ee was obtained in 60% yield. A much more efficient

enantioselective inclusion in the solid state was observed for oxime 9. A mixture of 2 and rac-

9 was irradiated with ultrasound (28 kHz) for 8 h, and the reaction mixture was washed with

light petroleum to leave an insoluble 1:1 complex of 2 and (+)-9 in 95% yield, which upon

treatment with H2SO4 in the solid state according to the reported method (ref. 8) gave the

Beckmann rearranged product (+)-1 0 of 79% ee in 68% yield. Therefore, the optical purity of

the (+)-9 in the complex with 2 should be higher than 79% ee.

When resolution in the solid state is combined with distillation, both enantiomers can be

separated easily by fractional distillation. For example, heating a mixture of powdered 2 and

rac-11 at 80 •Ž/1 mmHg gave (-)-11 of 68% ee in 121% yield by distillation, and further

heating of the residue at 150•Ž/1 mmHg gave (+)- 11 of 95% ee in 63% yield (ref. 9).

Improvement in the efficiency of resolution by distillation was achieved for p-methyl-

phenethylamine (12). Heating of a mixture of 3c and two molar amounts of rac-12 at 70•Ž/2

mmHg gave (+)-12 of 98% ee in 102% yield, and further heating of the residue at 150 •Ž/2

mmHg gave (-)-12 of 100% ee in 98% yield (Fig. 2). A certain economy about the latter

procedure was that the recovered 3c could be used again. The resolution method by distillation

is applicable to various kinds of compounds, namely, epoxides, epoxy-ketones, alcohols, alkyl

hydroxyoxycarboxylates, amino alcohols, and amines. Of course, this separation method of

enantiomers by distillation can be applied for the separation of isomers which have the same or

very similar boiling points.

4. Solid-Solid Reactions

When molecular movement occurs between substrate crystal and reagent crystal, an organic

reaction is expected to occur efficiently and selectively. In fact, various kinds of organic

reactions have been found to occur in the solid state. When a selective reaction, for example,

an enantioselective reaction, is desired, the selectivity can be controlled by using an optically

Fig. 2. Optical resolution of 12 by fractional distillation in the presence of the chiral host 3c

926

( 54 ) J. Synth. Org. Chem., Jpn.

active host compound.

The pinacol rearrangement is usually carried out under drastic conditions such as heating in

H2SO4. It was observed that the reaction proceeds faster and more selectively in the solid

state. Passage of dry HC1 gas through a flask containing finely powdered pinacol at 20-80•Ž

gave the rearranged products in good yields (ref. 10). p-TsOH-catalyzed Meyer-Schuster

rearrangement of 13 to 14 occurred efficiently at 50 •Ž in the solid state (ref. 11). Gaseous

HC1 or CC13COOH-catalyzed dehydration of 15 to 16 in the solid state also occurred very

efficiently at room temperature (ref. 11). When the alcohol 17 was treated with HC1 gas in the

solid state, the pure corresponding chlorides 18 were obtained in quantitative yield (ref. 11).

This procedure is applicable to the preparation of tent-butyl chloride.

13 14 15 16

17 18

The solid state etherification of alcohols is a reaction which has warranted considerable

interest. Treatment of benzhydrol (19) with p-TsOH in the solid state gave the ether 20. The solid state reaction was much faster than that in solution. This is due to a convenient molecular

arrangement of 19 in the crystal for the etherification reaction. X-ray crystal structure analysis

of 19 showed that two 19 molecules form a pair through hydrogen-bond formation in crystal

(Fig. 3) (ref. 11). These data suggest that the SN2 type reaction of 19 in the solid state may

proceed through a steric course whereby the configuration of the alcohol is retained. Mechanistically 19 only has one attack site available to its hydrogen bonding partner, thus the

attacking is limited to the front-side of the molecule and hence the configuration of the alcohol

should be retained.

19 20

The benzylic acid rearrangement is yet another reaction which we can add to our list of

efficient solid state reactions. In some cases, the rearrangement in the solid state is much faster

Fig. 3. A pair of benzhydrol molecules (19) in crystal


( 55 ) 927

than in solution. For example, a mixture of finely powdered benzil (21) and KOH was heated

at 80 •Žfor 0.2 h, and the reaction mixture was mixed with HC1 to give benzylic acid (22) in

90% yield (ref. 12). Similar treatment of various benzil derivatives in the solid state also gave

the corresponding benzilic acids (ref. 12). This method is much simpler than the usual one

which is carried out by heating benzil and alkali metal hydroxide in aqueous organic solvent.

The effect of the alkali metal hydroxide on the rate of the rearrangement in the solid state is

different from that in solution. The effect on the rate of the rearrangement of 21 in the solid

state increased in the order: KOH•„Ba(OH)2•„RbOH•„NaOH•„CsOH. On the other hand, the

rate of the rearrangement of 21 in boiling aqueous EtOH and 21 in 67% aqueous dioxane

incresed in the order: KOH•„NaOH•„Sr(OH)2•„Ba(OH)2•„CsOH, and LiOH•„NaOH•„CsOH•„-

KOH, respectively (ref. 13). The rearrangement by RbOH and Ba(OH)2 proceeded faster in

the solid state than in solution. However, LiOH and Sr(OH)2 were ineffective towards

rearrangement in the solid state, although these were active in solution (ref. 12).

21 22

The scope of solid state reactions was found to include even Grignard reactions. Dried

Grignard reagents were prepared as white powders by evaporation of the solvent in vacuo of

the reagents prepared by standard procedure in ether solvent.. When a mixture of one mole of

powdered benzophenone and three moles of EtMrBr was kept at room temperature for 0.5 h,

1,1-diphenylethanol and benzhydrol (19) were obtained in 30 and 31% yields, respectively

(ref. 14). When the same reaction was carried out in ether, yields of the former and latter were

80 and 20% yields, respectively. More of the reduction product was obtained in the solid state

than in solution. A plausible explanation for the difference is that the less hindered hydrogen

radical moves more easily in the solid state than does the alkyl radical.

In most cases, the Baeyer-Villiger oxidation reaction of ketones proceeds much faster in the

solid state than in solution. When a mixture of powdered benzyl phenyl ketone and m-

chloroperbenzoic acid was kept at room temperature for 24 h, benzyl benzoate was obtained in

97% yield. The same treatment of benzophenone gave phenyl benzoate in 85% yield (ref. 15).

When the reaction was carried out in CHCl3, benzyl and phenyl benzoate were obtained in 46

and 13% yields, respectively.

Another area of solid state chemistry which has emerged is the oxidative coupling reaction

of acetylenic compounds using copper salt in the solid state (ref. 16,17) and some notable

cases of selectiveities have been observed. For example, although the coupling of (-)-3,6-di-

tert-butyl-1,4,7-octatriyne-3,6-diol (23) in pyridine using Cu(OAc)2•EH2O gave an optically

active polymer 2 4, of relatively high molecular weight (Mn = 16,700) which consists of about

a hundred monomer units (ref. 16), that in the solid state gave optically active diner 2 4 (n = 2)

(ref. 17).

928

( 56 ) J. Synth..Org. Chem., Jpn.

2 3 2 4

It was further found that some oxidative coupling reactions of phenols with FeC13 proceed

faster and more efficiently in the solid state than in solution. When a mixture of finely

powdered 2-hydroxynaphthalene (25) and FeCl3 6H2O was kept at 50•Ž for 2 h, 2,2'-

dihydroxy-1,1'-binaphthyl (26) was obtained in 95% yield (ref. 18). When the reaction was

carried out in boiling aqueous EtOH, 26 was obtained only in 65% yield. As an extension of

this solid state reaction we have applied it to the oxidative coupling of various kinds of phenol

derivatives (ref. 18).

25

26

Previously, we have reported that Zn-ZnCl2 is an effective reagent for the reduction of

activated olefins (ref. 19) and ketones (ref. 20). We further found that the reagent is effective for the coupling of aromatic aldehydes and ketones to produce a-glycols in the solid state.

When a mixture of benzaldehyde (27a), Zn, and ZnCl2 was kept at room temperature for 3 h,

benzpinacol (28a) was obtained in 46% yield as the sole isolatable product. In other analogous reactions, 27b and 27c gave 28b (87%) and 28c in 87% and 65% yields,

respectively. When the reaction was carried out in 50% aqueous THF, 28a, 28h, and 28c

were obtained only in 11, 7, and 16% yields, respectively, and the reduction products, the

corresponding alcohol derivatives were found to be the major product (ref. 21). Reformatsky and Luche reactions with Zn provide a more economical method for C-C bond

formation than the Grignard reactions requiring the expensive Mg metal. In addition, we found

that both Reformatsky and Luche reactions proceed efficiently in the absence of solvent. The

nonsolvent Reformatsky and Luche reations can be carried out by .a very simple procedure and

give products in higher yield than with solvent. In general, the nonsolvent reaction was carried out by mixing aldehyde or ketone, the appropriate organobromide compound, and Zn-NH4C1

using an agate mortar and pestle and keeping the mixture at room temperature for several hours. Treatment of the aromatic aldehydes 27a, 27d, and 27e with ethyl bromoacetate (29)

and Zn-NH4C1 gave the corresponding Reformatsky reaction products, 30a (91%), 30d

(94%), and 30e (83%), respectively in the yields shown (ref. 22). The yield, for example, of 30a obtained in the nonsolvent reaction (91%) is much better than that obtained by the reaction

in dry benzene-ether solution (61-64%) (ref. 23). The nonsolvent Reformatsky reaction,

which does not require the use of an anhydrous solvent, is thus advantageous. Synthesis of

Vol.52, No.11 (November 1994) ( 57 ) 929

homoallylic alcohols by the Luche reaction (ref. 24) can also be carried out efficiently in the

absence of solvent. Treatment of 3-bromopropene (31) with various carbonyl containing

substrates, namely benzaldehyde (27a), cyclohexanone, and hexanal in the presence of Zn-

NH4Cl but in the absence of solvent, gave the corresponding Luche reaction products, 32a

(99%), 3 3 (90%), and 3 4 (83%), respectively in the yields indicated (ref. 23).

2728

29 30

31 32

33 34

Methylene transfer reactions from ylide to electrophilic unsaturated linkages, C=C, C=O,

and C=N, are useful methods for the synthesis of cyclopropanes, oxiranes, and aziridines,

respectively. As a source of active methylene, dimethylsulfonium methylide (36) which is

generated from trimethylsulfonium iodide (3 5) by treatment with NaH in dry THE has been reported (ref. 25). However, the procedure for preparing the ylide is rather laborious and

therefore we have developed a very simple methylene transfer reaction procedure which can be

carried out in the solid state. For example, a mixture of powdered chalcone 37a, 35, and

KOH was kept at room temperature for 3 h, the mixture was then washed with water, and the

residue was worked up in the usual manner to give the trans-l-benzoy1-2-phenylcyclopropane

(38a) in 79% yield. By similar treatment, 37 b -e gave the corresponding cyclopropane derivatives 38b-e in 91, 79, 82, and 81% yields, respectively (ref. 26). Similar treatments of

ketones (39) and imines (41) gave oxiranes (40) and aziridines (4 2), respectively (ref. 23).

35 36

37 38

39 40 41 42

930


5. Enantiocontrol of Solid-Solid Reactions

When solid-solid reactions are carried out in an inclusion crystal with a chiral host, the

reactions can be controlled to proceed enantioselectively.

NaBH4 reduction of ketones to alcohols in the solid state has been reported (ref. 27). In

order to carry out the reaction enantioselectively, the inclusion crystal of ketone 43 and 2 was reacted with borane-ethylenediamine complex, 2BH3-NH2CH2CH2NH2 in the solid state,

and optically active alcohols 44 were obtained (Table 1) (ref. 28). Indeed it is a valuable

finding that the solid state reaction can be used even for enantioselective synthesis.

43 44

NaBH4 reduction of 4 3 mediated in the presence of ƒÀ-cyclodextrin also proceeded quite

easily in the solid state. However, the product alcohol 44 in all cases gave modest levels of

optical purity only (ref. 29).

We also found that Wittig-Horner reaction can be carried out enantioselectively in an

inclusion crystal with 3 (ref. 30). When a mixture of finely powdered 1:1 inclusion compound

of 3b and 4-methylcyclohexanone (45a) and (carbethoxymethyl)triphenylphosphorane,

Ph3P=CHCOOEt was kept at 70 •Ž, the Wittig-Horner reaction was completed within 4 h, and

(-)-4-methyl-1-(cabethoxymethylene)cyclohexane (4 6a) of 42.3% ee was obtained in 73%

yield. By the same procedure, 45 b and 47 gave optically active Wittig-Horner reaction

products, 46b of 45.2% ee (72.5% yield) and 48 of 56.9% ee (58% yield), respectively, in

the yields indicated (ref. 30).

Table 1. Yield, optical purity, and absolute configuration of the alcohol 44 obtained by

solid-solid reaction of a 1:1 inclusion crystal of 2 and 4 3 with 2BH3•ENH2CH2CH2NH2


( 59 ) 931

4 5 4 6

4 7 4 8

The Michael addition of thiol derivatives (50) to 2-cyclohexenone (49) included in 3c in the

solid state proceeded enantioselectively (ref. 31). For example, when a mixture of powdered

1:1 inclusion crystal of 49 and 3 c, along with 2-mercaptopyridine (50a), and a catalytic

amount of benzyltrimethylammonium hydroxide, PhCH2N+Me3 OH- was irradiated with

ultrasound (28 kHz) for 1 h at room temperature, (+)-5 1a of 80% ee was obtained in 51%

yield. Similar treatments of the inclusion complex of 49 and 3c with 50b, 50c, and 50d

gave 51 b of 78% ee (58%), 51c (58%, optical purity was not determined), and 51 d of 74% ee (77%), respectively, in the yields indicated. The Michael addition of 50a and 50c to 2- methyl-1-buten-2-one (52) included in 3c gave (+)-53a of 49% ee and (+)-5 3c of 53% ee in

76% and 78% yields, respectively (ref. 28).

49 50 51 52 53

6. Photoreactions in Inclusion Crystal

The most successful reaction controls in the inclusion crystal were achieved by the solid

state photoreaction. These data are summarized in reviews (ref.32).

7. Conclusion

The discovery of selective molecular movement from crystal to crystal led to the

establishment of a new optical resolution method by distillation and selective solid-solid organic reactions. There are many possibilities for the further development of new organic

932 ( 60 ) J. Synth. Org. Chem., Jpn.

chemistry by utilizing this fascinating phenomenon. Therefore it is needless to say that our long term objective is to establish solid state organic chemistry as a new field in chemistry.

References and Notes

(1) Toda, F.; Akagi, K. Tetrahedron Lett. 1968, 3695.

(2) Toda, E; Tanaka, K.; Wang, Y.; Lee, G.-H. Chem. Lett. 1986, 109.

(3) Toda, F.; Tanaka, K.; Nakamura, K.; Ueda, H.; Oshima, T. J. Am. Chem. Soc. 1983, 105, 5151.

(4) Seebach, D.; Beck, K.; Imwinkelried, S.; Roggo, S.; Wonnacott, A. Helv. Chim. Acta 1987, 70 , 954. Toda, F; Tanaka, K. Tetrahedron Lett. 1988, 29, 551.

(5) Toda, F.; Tanaka, K.; Miyahara, I.; Akutsu, S.; Hirotsu, K.J. Chem. Soc., Chem. Commun. 1994, in press.

(6) Toda, F; Tanaka, K.; Sekikawa, A. J. Chem. Soc., Chem. Commun. 1987, 279.

(7) Tanaka, K.; Toda, F. J. Chem. Soc., Chem. Commun. 1983, 593. Tanaka, K.; Toda, F. Nippon Kagaku Kaishi 1984, 141. Kaftory, M.; Tanaka, K.; Toda, E J. Org. Chem. 1985,

50, 2154.

(8) Toda, Akai, H. J. Org. Chem. 1990, 55, 4973.

(9) Toda, F; Tohi, Y. J. Chem. Soc., Chem. Commun. 1993, 1238. Kaupp, G. Angew. Chem. Mt. Ed. Engl. 1994, 33, 728.

(10) Toda, F; Shigemasa, T. J. Chem. Soc. Perkin Trans. 1 1989, 209. (11) Toda, F; Takumi, H.; Akehi, M. J. Chem. Soc., Chem. Commun. 1990, 1270.

(12) Toda, F.; Tanaka, K.; Kagawa, Y.; Sakaino, Y. Chem. Lett., 1990, 373.

(13) Puterbaugh, W. H.; Gaugh, W. S. J. Org. Chem. 1961, 26, 3513.

(14) Toda, F; Takumi, H.; Yamaguchi, H. Chem. Exp. 1989, 4, 507.

(15) Toda, Yagi, M.; Kiyoshige, K. J. Chem. Soc., Chem. Commun. 1988, 958.

(16) Toda, F; Okada, K.; Mori, K. Angew. Chem. Mt. Ed. Engl. 1988, 27, 859.

(17) Toda, F,; Tokumaru, Y. Chem. Lett. 1990, 987.

(18) Toda, F; Tanaka, K.; Iwata, S. J. Org. Chem. 1989, 54, 3007. (19) Toda, F.; Iida, K. Chem. Lett. 1978, 695.

(20) Toda, F; Tanaka, K.; Tange, H. J. Chem. Soc. Perkin Trans. I 1989, 1555.

(21) Tanaka, K.; Kishigami, S.; Toda, E J. Org. Chem. 1990, 55 , 2981. (22) Tanaka, K.; Kishigami, S.; Toda, E J. Org. Chem. 1991, 56, 4333.

(23) Hauser, C. R.; Breslow, D. S. Org. Synth. 1941, 21, 51.

(24) Petrier, C.; Luche, J.-L. J. Org. Chem. 1985, 50, 910.

(25) Corey, E. J.; Chaykowsky, M. J. Am. Chem. Soc. 1965, 87, 1353.

(26) Toda, F; Imai, N. unpublished data.

(27) Toda, F; Kiyoshige, K.; Yagi, M. K. Angew. Chem. Mt. Ed. Engl. 1989, 28, 320.

(28) Toda, F; Mori, K. J. Chem. Soc., Chem. Commun. 1989, 1245.


( 61 ) 933

(29) Toda, F.; Shigemasa, T. Carbohyd. Res. 1989, 192, 363.

(30) Toda, E; Akai, H. J. Org. Chem. 1990, 55, 3446.

(31) Toda, F.; Tanaka, K.; Sato, J. Tetrahedron Asymm. 1993, 4, 1771.

(32) Toda, F. Top. Curr. Chem. 1988, 149, 211. Toda, F. Bioorg. Chem.1991, 19, 157. F. Toda, In Advances in Supramolecular Chemistry Vol. 2, Gokel, G., Ed.; JAI Press Inc:

London, 1992, 141.

(Received June 27, 1994)

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Organic Reactions in Crystals