112 E. I. KLABUNOVSKli 



extended their application to the absolute asymmetric synthesis of a-/3-diphenyl- 

 propionic acid by hquid-phase hydrogenation of a-phenylcinammic acid, and 

 that of optically active pinane from a-pinene. 



Ponomarev & Zelenkova [60] used nickel on quartz for the asymmetric syn- 

 thesis of a number of derivatives of furane. The reactions occurred under 

 pressure at 120 °C. From i-(a-furyl)-propan-3-ol they obtained optically active 

 i-tetrahydrofuryl-propan-3-ol and I : 6-dioxa5/)2ro(4 : 4)nonane; while from i- 

 (a-furyl)-butan-3-ol they obtained optically active i-tetrahydrofurylbutan-3-ol 

 and 2-methyl-i : 6-dioxa5p/ro(4 : 4)nonane. 



The action of the catalyst in evoking dissymmetry in these cases resembles 

 that of reductase. 



Using a catalyst (alkaU on quartz) it has been possible to bring about the 

 asymmetric, liquid-phase cyanethylation of 2-methylcyc/ohexanone. This differs 

 essentially from the reactions previously considered in that it does not require a 

 high temperature but takes place at 20-30 °C, i.e. under the same conditions as 

 enzymic syntheses in nature [61, 43] : 



CH3 ,, / \CH3 



c c 



H C 



From what has been said it is seen that much material has been collected with 

 reference to the imitation of the asymmetric action of enzymes. 



Chemical models of enzymes have an interesting pecuUarity: the range of 

 their actions is incomparably greater than that of the enzymes while they are 

 not so stereospecific. If a particular enzyme is capable of carrying out the re- 

 actions described under one heading in the index, then the corresponding organic 

 catalyst will be able to bring about reactions of a completely different type with 

 a fair degree of specificity. 



Table 2 shows the enzymes, the index of their reactions and their chemical 

 counterparts which have a comparable action. 



Clearly, if the model of the enzyme has a relatively simple structure (deri- 

 vatives of camphor), it will be hard to distinguish the parts of the molecule 

 corresponding with the coenzyme or apoenzyme. Even in the case of the quinine 

 alkaloids it has been possible to show that, for example, in the cyanhydrin syn- 

 thesis, it is only the C-9 configuration in the molecule which determines the 

 asymmetric synthesis of the oxynitrile [53]. In the case of heterogeneous catalysts 

 it is easier to distinguish the evocation of dissymmetry from the act of catalysis 

 since dissymmetry is evoked by asymmetric adsorption. 



The results obtained by the use of catalysts, and, in particular, quartz catalysts, 

 as chemical models of enzymes are of great theoretical interest in that they reveal 

 the possibihty of creating a new type of heterogeneous model of enzymes. Further- 

 more, the bringing about of absolute asymmetric syntheses and asymmetric de- 

 composition of racemates, by the use of metals deposited on optically active 



