The synthesis and chemistry of azolenines. Part 8. The Paal-Knorr reaction with cyclic 2-(acylmethyl)-2-alkyl-1,3-diketones: isolation of 1-acyl-1H-pyrroles via rearrangement
Abstract
Treatment of cyclic 2-acylmethyl-2-alkyl-1,3-diketones with ammonium acetate under reflux in acetic acid gives moderate to high yields of 1-acyl-1H-pyrroles by rearrangement. Some of the cyclic diketones react quantitatively with liquid ammonia to yield 2-hydroxy-3,4-dihydro-2H-pyrroles, which are converted in high yields into 1-acyl-1H-pyrroles by a number of methods. Possible mechanisms for the rearrangement are discussed, a process involving transannular interaction within an eight- or nine-membered ring being favoured. Improved methods for the mono- and bis-C-alkylation of cyclic 1,3-diketones are also described.
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