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Synthesis of Substituted Pyrroles from 2-Azetidinone Allenols
B. Alcaide*, P. Almendros, R. Carrascosa, M. C. Redondo
Universidad Complutense de Madrid, Spain
21 February 2008 (online)
Reported is the formation of highly substituted pyrrole systems by reaction of β-lactams with sodium methoxide. The required β-lactams were formed through an indium-mediated Barbier-type allenylation reaction previously developed by the authors. Reaction of these allenyl β-lactams with sodium methoxide opens the lactam ring to a secondary amine, which then undergoes reaction with the allene to form the desired pyrrole ring upon workup. Two examples of the intermediate amine (structures A above) were isolated and cyclized to pyrroles using catalytic silver nitrate. All other analogues examined spontaneously formed pyrroles under the sodium methoxide reaction conditions.