[4-CYCLOADDITION REACTIONS BETWEEN BETA-ACCEPTOR-SUBSTITUTED ENAMINESAND 2-VINYLINDOLE RADICAL CATIONS ACTING AS HETERO-DIENES(2])

[4 + 2]-Cycloaddition reactions between 2-vinylindoles acting as heter o-dienes and P-acceptor substituted cyclic and acyclic enamines can be induced by formation of 2-vinylindole radical cations either via anod ic oxidation or photoelectron transfer (PET) using catalytic amounts o f triarylpyrylium tetrafluoroborates as sensitizers. In this way, pyri do[1,2-a]indoles or indolo[1,2-a]hexahydro-1,8-naphthyridines are form ed in one step with complete regio- and stereochemical control.