Enantioselective Robinson Annelations via Phase‐Transfer Catalysis

Abstract

Alkaloids as chiral phase transfer catalysts effect enantioselective alkylation of 1, R = Pr, with the methyl vinyl ketone synthetic equivalent 1,3-dichloro-2-butene to give 2, R1 = Pr, R2 = CH2CH = C(Cl)CH3. The two enantiomers are obtained with 92 and 78% ee, respectively, and, in each case, in 99% yield; cinchoninium and cinchonidinium derivatives serve as catalysts. The results are explained in terms of an intermediate formation of a tight ion pair.