Preparation of caffeic and dihydrocaffeic acids by methods suitable for introduction of C14 into the beta-position.

3,4-(Dibenzyloxy)-benzoyl chloride (m.p. 95°) was prepared from the corresponding acid, and reduced to 3,4-(dibenzyloxy)-benzaldehyde (m.p. 86°) by Rosenmund's method. The over-all yield of this aldehyde was 52%, based on the barium carbonate used for preparation of the acid. The aldehyde was debenzylated by hydrogen bromide in acetic acid, and the protocatechualdehyde thus obtained was condensed with malonic acid, to give caffeic acid. Condensation of 3,4-(dibenzyloxy)-benzaldehyde with malonic acid gave 3,4–(dibenzyloxy)-cinnamic acid (m.p. 206–208°) which was converted to dihydrocaffeic acid by catalytic hydrogenation. The over-all yields of caffeic and dihydrocaffeic acids were 36% and 39%, respectively, based on barium carbonate. Protocatechuic acid was readily obtained by hydrogenolysis of 3,4-(dibenzyloxy)-benzoic acid; the yield was 70% based on carbonate.