Polyene acids. Part 11. Preparation of α-tritiated (or deuteriated) conjugated enoic and dienoic acids and their examination by triton magnetic resonance spectroscopy

Abstract

Decarboxylation in boiling pyridine of conjugated ene[OO′-³H]dioic acids (from aryl or alkyl aldehydes and malonic acid, followed by exchange tritiation with labelled water) efficiently provided α-tritiated trans-αβ-unsaturated acids. Extended to croton- and cinnam-aldehydes, the method yielded conjugated dienoic acids labelled at both α- and γ-positions as shown by ³H n.m.r. Labelling at only the α-position was achieved by thermal monodecarboxylation of the intermediate from cinnamaldehyde. Mechanisms are discussed. Similar reactions can be used for the preparation of deuteriated αβ-unsaturated acids.