Absolute Asymmetrie Synthesis and Asymmetrie Catalysis 



163 



The action of the catalyst, in this case, resembles that of carboxylase. The 

 action of alkaloids on the asymmetric reduction of /3-methyl- and ^-(a-naphthyl)- 

 cinnamic acid in the presence of hydrocinchonine [46] would appear to be 

 analogous, as would their action in the bromination of cinchonine salts of cin- 

 namic acid or glucosamine cinnamate [47]. 



There is, of course, a catalytic action by alkaloids which is even more like that 

 of enzymes. It is seen in cases when the possibility of the formation of individual 

 chemical compounds is ruled out. There are many such examples [48] of the 

 formation of an excess of one antipode of esters by the catalytic action of 

 brucine or strychnine. They are obtained by acetylation or benzoylation of 

 racemic secondary alcohols or by the esterification of racemic chloranhydrides 

 of acids. 



The dehydration of methylphenylcarbinol [49] also belongs to this group of 

 reactions; it occurs in the presence of 2% camphorsulphonic acid with the 

 formation of the optically active oxide. The asymmetric dehydration of a di- 

 phenyldinaphthylallyl alcohol with the formation of a substituted aliène [50] has 

 also been reported. 



The general nature of the index is such that, in spite of their variety, all these 

 reactions belong to the group of reactions catalysed by esterases. 



(+)-Camphorsulphonic acid is of special interest, being an asymmetric 

 catalyst which, besides acting as an esterase, can also function asymmetrically 

 as a ketoaldomutase. Asymmetric synthesis in the flavone series can be brought 

 about by the catalytic action of (+)-bromocamphorsulphonic acid. 



Optically active 4'-methoxy-5 : 6-benzoflavonone has been obtained by the 

 method of Fujise & Sasaki [51]. (+)-7-Hydroxyflavone was obtained from 2 : 4- 

 dihydroxychalcone, and (+)-6 : 8-dimethyl-5 : 7-diacetoxy-4'-methoxj^avone 

 was obtained from 2' : 4' : 6'-triacetoxy-3' : 5'-dimethyl-4-methoxychalcone. 



H— 1 -=^ ">\ /^ H- 



H\ C 

 CH30-CeH4- 



CH30-C6H4- 



A chemical model of oxynitrilase is provided by the catalytic action of the 

 cinchona alkaloids in the synthesis of the partially optically active nitrile of 

 mandeUc acid from benzaldehyde and HCN. This reaction extends to cover 

 other aldehydes, including cinnamic aldehyde, anisic aldehyde, citral, piperonal 

 and acetaldehyde [52]. 



Prelog & Wilhelm [53] have made a detailed study of the influence of the struc- 

 ture and of the configuration of the molecules of catalysts (derived from quinine 

 and quinidine) on the efficiency of the asymmetric cataljrtic synthesis of the 

 nitriles of benzallactic and mandelic acids : 



C6H5CH:CHCHO + HCN 

 CeHsCHO + HCN 



CeHs • CH :CH • CH(OH) • CN 

 C6H5CH(OH)CN. 



A definite relationship has been estabUshed between the spatial structure of 

 the catalyst and that of the product. 



