Unsaturated lactones and mercaptans. Part III. Lactam of 2-(β-carboxyethyl)-2-methylthiazolidine-4-carboxylic acid from α-angelica lactone (pent-3-en-4-olide) and cysteine, and its n.m.r. spectrum

Abstract

The reaction product from α-angelica lactone (pent-3-en-4-olide) and cysteine was considered by Cavallito and Haskell to be an eight-membered ring lactam; Black has recently found supporting evidence for this. Reinvestigation by n.m.r., however, reveals the compound to be the lactam of 2-(β-carboxyethyl)-2-methylthiazolidine-4-carboxylic acid. The reaction proceeds in two steps and a mechanism leading to this unexpected structure is given. The identity between this compound and the one from 4-oxopentanoic acid and cysteine is demonstrated.