Generation and cycloaddition of heteroatom-substituted 2-azaallyl anions with alkenes and alkynes. Synthesis of 1-pyrrolines and pyrroles

Abstract

Imidates and thioimidates 1 bearing an N-(1-tri-n-butylstannyl)alkyl group (e.g., 7-9) were transmetalated with n-BuLi to generate heteroatom-substituted 2-azaallyl anions 2. These anions underwent [2[pi]s+4[pi]s] cycloadditions with alkenes to produce 1-pyrrolines 4 after loss of alkoxide or thiolate. The pyrrolines were further deprotonated in situ with n-BuLi to generate 1-metalloenamines 5, which could be quenched with water or CH3I to produce 1-pyrrolines 4 or 6. The use of diphenylacetylene in the cycloaddition resulted in the formation of a pyrrole.