Synthesis of Bisbenzil Isomers and Derivatives.

摘要

The goal of this investigation was to apply the modified benzoin condensation, used successfully in the synthesis of unsubstituted para-bis(phenylglyoxyloyl) benzene, to the preparation of substituted para-derivatives as well as to the production of selected meta and ortho isomers. Using this process the substituted compounds: p-bis(p-methoxyphenylglyoxyloyl) benzene, p-bis(p-hydroxyphenylglyoxyloyl)benzene, and p-bis(p-chlorophenyl-glyoxyloy) benzene, were obtained yields of 41, 16, and 46%, respectively. The formation of the bis-cyanohydrin intermediate was unequivocally proven by its transformation to the para-bis-hydroxy acid. The extension of the modified benzoin reaction to the synthesis of meta and ortho isomers of p-bis(phenylglyoxyloyl)benzene was to date unsuccessful. In the case of isophthalaldehyde the intermediate bis-cyanohydrin was unexpectedly stable, which under the conditions employed prevented its condensation with benzaldehyde. This material was characterized by the hydrolysis to the meta-bis(hydroxy acid). Reaction of benzaldehyde cyanohydrin with isophthalaldehyde resulted in hydrogen cyanide exchange and formation of the bis-cyanohydrin of isophthalaldehyde and benzaldehyde. The cyanohydrin derived from phthalaldehyde appeared to undergo self-condensation above 0 C; at lower temperatures no reaction with benzaldehyde occurred. (Author)