π‐Lewis‐Base‐Catalyzed Asymmetric Vinylogous Umpolung Reactions of Cyclopentadienones and Tropone

Abstract

We disclose that the carbonates of 4-hydroxy-2cyclopentenones can form p-allylpalladium-based 1,2-carbodipoles,w hichi somerizet oi nteresting h 2 -Pd 0 -cyclopentadienone complexes.C ompared with the labile parent cyclopentadienone,t he HOMO energy of the related h 2 -complex was significantly raised via the back-bonding of Pd 0 as a p-Lewis base,r endering the uncoordinated C=Cb ond an electronricher dienophile in inverse-electron-demand aza-Diels-Aldertype reactions with diverse 1-azadienes.T he vinylogous (aza)Morita-Baylis-Hillman or cross Rauhut-Currier addition to (imine)carbonyls or activated alkenes,respectively,was also realized to affordc hiral [4+ +2] or [2+ +2] cycloadducts, respectively,a fter trapping the re-generated p-allylpalladium species.N ew C 1 -symmetric ligands from simple chiral sources were developed, exhibiting high stereoselectivity even with racemic substrates via an unusual dynamic kinetic resolution process.Besides,tropone could be similarly activated by aPd 0 complex.Scheme 1. Different strategies for umpolung reactions of electron-poor alkenes.