Reactions of 3,4-dehydroproline and 4-chloroprolines with ninhydrin, isatin, and cyclic α-diketones

Abstract

3,4-Dehydro-DL-proline reacts with a number of a-dicarbonyl compounds to form products in which the pyrroline ring is converted into an N- substituted pyrrole. Depending on the reactivity of the α-dicarbonyl compound, a second molecule may (e.g. ninhydrin) or may not (e.g, isatin) react further by α-substitution of the pyrrole. The structures of the products account for the different colour reactions of dehydroproline compared with proline. cis- and trans-4-Chloro-L-proline yield the same products as dehydroproline with ninhydrin and isatin.