Novel Hybrid Prins/Aza-Prins Oxocarbenium/N-Acyliminium Cascade Expedient Access to Complex Indolizidines

Abstract : Heavy silyl enol ethers (mostly TIPS and TBS) combine with cyclic N-alkenyl N-acyliminium salts generated in situ from their N,O-acetal precursors, to furnish highly functionalized indolizidines through an unprecedented double Mukaiyama–Mannich–Prins cascade transformation. This novel cascade annulation process demonstrates a promising scope, and takes place mostly catalytically with interesting stereocontrol. Furthermore, an appealing facet of this chemistry is emphasized with a bicatalytic approach by which the Mannich–Prins cascade follows a Ru-catalyzed N-allylamide to N-(E)-propenyl isomerization of the aminal counterpart in a one-pot operation. © 2018 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim