Synthesis of Substituted Pyrroles from 2-Azetidinone Allenols

Significance

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.