Synthesis of new chiral N-heterocyclic carbenes from naturally occurring podophyllotoxin and their application to asymmetric allylic alkylation

Chiral N-heterocyclic carbenes (NHC) were synthesized from naturally occurring podophyllotoxin. Their coordination with [(η3-allyl)Pd(Br)]2 afforded (NHC)Pd(allyl)Br complexes, whose structures were unambiguously established by X-ray single crystal analysis. These chiral NHC and NHC-Pd-allyl complexes were found to catalyze the substitution reaction of allylic compounds with high conversions and enantioselectivities (up to 87% ee).

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(R,E)-Diethyl 2-(1,3-diphenylallyl)malonateC22H24O4Ee = 87%[α]D25=+15.1 (c 1.40, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (R)