CHA-initiated [3 + 2 + 1] spiroannulation of enaminone with diazo oxindole leading to a concise and divergent synthesis of oxindole spirohydropyridines

Abstract

Presented herein is a concise and divergent synthesis of oxindole spirohydropyridine derivatives based on the reaction of enaminone with diazo oxindole. In forming the hydropyridine skeleton, one enaminone acts as a C2N1 synthon and another enaminone acts as a C2 synthon, while diazo oxindole acts as a C1 synthon. Interestingly, by altering the substructure of enaminone, a spirotetrahydropyridine or spirodihydropyridine scaffold could be constructed in a highly selective manner. To the best of our knowledge, this is the first report on the synthesis of diversely substituted oxindole spirohydropyridine derivatives based on an alkenyl C–H bond activation-initiated cascade reaction of enaminone with a diazo compound. In general, this novel protocol features simple and affordable substrates, valuable products, a concise one-pot procedure, an intriguing reaction pathway, excellent selectivity, good step- and atom-economy, and ready scalability.