Seven-Membered Azacyclic Allenes: Synthesis, Trapping, and Stereochemical Transfer Studies

Methods for the synthesis of functionalized seven-membered rings, especially those containing nitrogen atoms, are underdeveloped but remain coveted. We report the chemistry of seven-membered azacyclic allenes as a means to access ring-fused azepanes that possess up to three newly formed stereocenters. We demonstrate that seven-membered azacyclic allenes outperform their six-membered counterparts in enantiospecific cycloaddition studies, consistent with computational predictions of enantiomerization barriers. Beyond providing a practical method for annulated azepane synthesis and elucidating selectivity trends, our findings offer insight into the interplay between cyclic allene ring size and enantiospecificity in trapping experiments. These studies are expected to further enable the use of strained cyclic allenes in synthesis.