Stereochemical Analysis of the Enzymic Reduction of the Double Bond of α‐ and β‐Substituted Nitrostyrenes and α‐Ethoxycinnamaldehyde through Deuterium Labelling Experiments

Abstract 2H NMR studies and comparison with authentic labelled reference compounds prepared from the (Z)‐acetamido‐cinnamic acid 10 and from (Z)‐2‐ethoxy‐3‐(4‐methoxyphenyl)prop‐2‐en‐1‐ol (14), respectively, by catalytic syn reduction with deuterium gas show that the baker's yeast‐mediated saturation in the presence of deuterated water of the double bond of (E)‐α‐(hydroxymethyl)nitrostyrene (2) and of the (Z)‐α‐ethoxycinnamaldehyde (3) leads to (2R,3R)‐[2,3‐2H2]‐3‐(4‐methoxyphenyl)‐2‐nitropropan‐1‐ol (5) and to(1R,2S,3R)‐[1,2,3‐3H2]‐2‐ethoxy‐3‐(4‐methoxyphenyl)propan‐1‐ol (6), respectively, thus supporting an anti mode of hydrogen addition across the activated double bond, with hydride delivery in β‐position respect to the activating group from the upper side of the molecule.