Borylative Cyclization of 1,6-Allenynes Driven by BCl3.

A metal-free intramolecular borylative cyclization of 1,6-allenynes driven by BCl3 was developed. This method provides a general and practical strategy to construct valuable pyrrolidines containing all-carbon quaternary centers or 3,5-dihydroazepine derivatives depending on the substituents of the allene, with conjugative and sterically hindered phenyl groups favoring the latter.