Stereospecific hydrogenation of (Z)-α-benzoylamino-o-benzyloxy[β-2H]cinnamic acid

Abstract

Photoisomerisation of (Z)-4-(2-acetoxybenzylidene)-2-phenyloxazolin-5-one gave the E-isomer. The stereochemistry of each form was established by successive treatment with alkali and acid: the former gave an o-hydroxycinnamic acid and the latter a coumarin. Catalytic (10% palladium–carbon) hydrogenation of (Z)-α-benzoylamino-o-benzyloxy[β-²H]cinnamic acid and cyclisation (dicyclohexylcarbodi-imide) of the resulting phenolic acid gave 3-benzoylamino-3,4-dihydro[4-²H]coumarin. The trans-orientation of the hydrogen atoms in this product, revealed by n.m.r. spectroscopy, showed that hydrogenation of the cinnamic acid had occurred in a cis manner with high stereoselectivity.