Stereospecific Insertion of Cyclic Amidines into Aryl-Substituted Cyclopropanones: Access to Complex Spirocyclic Aminals

A facile, catalyst-free protocol to access structurally complex spirocyclic aminals from cyclopropanone surrogates and amidines is reported. The two-component reaction is described as a stereospecific insertion of the amidine C═N bond into the C1-C2 bond of the cyclopropanone via the addition of N to the carbonyl group, followed by ring enlargement. The products display similarities to numerous biologically active oligocyclic systems. Further structural diversification is demonstrated, and a proposed mechanism based on experimental and computational evidence is provided.