Synthesis and chemistry of azolenines. Part 16. Preparation of both 3H- and 2H-pyrroles from 2,2-disubstituted 1,4-diketones via the Paal-Knorr reaction, and isolation of intermediate 2-hydroxy-3,4-dihydro-2H-pyrroles

Abstract

Treatment of 2,2-disubstituted 1,4-diketones (1) with liquid ammonia gives high yields of isolable isomeric 2-hydroxy-3,4-dihydro-2H-pyrroles (10) and (11), many of which may be dehydrated to 3H-pyrroles (2) together, in certain cases, with isomeric methylene-pyrrolines (14) and (15). When heated in acetic acid with ammonium acetate, the diketones (1) yield 2H-pyrroles (18), sometimes in admixture with 3H-pyrroles (2) from which they are formed by rearrangement. The diketones (1), including some novel examples, are prepared from nitro-ketones (6) by the Nef reaction, as well as other methods.