Lewis Acid Catalyzed Cyclopropane Ring‐Opening‐Cyclization Cascade Using Thioureas as a N,N‐bisnucleophile: Synthesis of Bicyclic Furo‐, Pyrano‐, and Pyrrololactams via a Formal [4+1]‐Addition

Fused bicyclic cyclopropanes were converted by Lewis acid‐catalysis with thioureas to furo‐, pyrano, and pyrrololactams with yields of up to 99 % and high diastereoselectivity. The formation of the title compounds, representing a formal [4+1]‐cycloaddition to a donor‐acceptor substituted cyclopropane, follows a cascade reaction involving SN1‐type ring‐opening addition and cyclization. Thiourea, being a cost‐effective and odorless reagent, acts as an N,N‐bis‐nucleophile to generate bicyclic compounds containing an N‐substituted γ‐lactam moiety. A formal [4+1]‐cycloaddition of bicyclic D−A cyclopropanes and thioureas, acting as N,N‐bisnucleophiles, is developed to synthesize analogs of prevalent furolactones, i. e. furolactams and related heterocycles.