Palladium-catalysed asymmetric annulations of Morita-Baylis-Hillman carbonates with allenes or alkenes via migratory insertion

Abstract

As one of the most versatile intermediates in organic synthesis, π-allylpalladium complexes have been extensively exploited in allylic alkylation reaction with a wide range of nucleophiles. In contrast, their engagement in migratory insertion process remains significantly underdeveloped. Here we demonstrate that the π-allylpalladium intermediates derived from Pd⁰ and Morita-Baylis-Hillman (MBH) carbonates of activated ketones can isomerize to corresponding ƞ¹-form when stabilised by a pendent carbonyl group, and undertake migratory insertion into various allenes and even styrene-type alkenes efficiently.Subsequent vinylogous deprotonation of the newly formed multifunctional π-allylpalladium species followed by isomerization and intramolecular allylic alkylation leads to skeletally diverse (3+2) adducts with high levels of regio- and stereoselectivity. This catalytic strategy not only achieves migratory insertion of non-zwitterionic π-allylpalladium intermediates, but also overcomes the inherent limitations that the MBH carbonates can only undergo annulations with electrophilic dipolarophiles via Lewis base catalysis. Mechanistic insights are further elucidated through comprehensive density functional theory calculation studies.