Lewis acid-catalyzed intramolecular cyclization of 7-alkynylcycloheptatrienes with allenes: access to 1,2,3,4-tetrahydropyridines and 1,2,3,6-tetrahydropyridines.

Disclosed herein is a Lewis acid-catalyzed intramolecular cyclization of 7-alkynylcycloheptatrienes with allenes. A variety of highly functionalized 1,2,3,4-tetrahydropyridines were obtained in moderate yields. Subsequent tandem selective CC double bond reduction and isomerization of the products gave 1,2,3,6-tetrahydropyridines. Additionally, scale-up reactions and late-stage derivatizations highlight the potential synthetic utility of this methodology.