Pd-Catalyzed Dearomative [4 + 2] Annulation of 3-Substituted NH-Indoles with 2-Methylenepropane-1,3-diol and Its Mono-Aza Variant

Pd-catalyzed C3 allylation of indoles with allylic alcohols is well established; however, the use of allylic diols, such as 2-methylenepropane-1,3-diol, in the dearomative annulation of 3-substituted indoles remains unexplored. Herein, we report a Pd-catalyzed, Et3B-promoted alkylative dearomatization–cyclization cascade of 3-substituted NH-indoles using 2-methylenepropane-1,3-diol, enabling the one-step synthesis of hexahydropyrano[2,3-b]indoles in high yields and with full cis-diastereoselectivity. The method was further extended to the synthesis of cis-fused hexahydropyrido[2,3-b]indoles using the corresponding mono-aza analogue of the diol.