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γ-Alkylation of α-Branched Enals with Stable Carbocations
G. Bergonzini, S. Vera, P. Melchiorre*
Institució Catalana de Recerca i Estudis Avançats, Barcelona and Institute of Chemical Research of Catalonia, Tarragona, Spain
21 December 2010 (online)
The asymmetric vinylogous γ-alkylation of α-branched enals with bis-(4-dimethylaminophenyl)-methanol is reported. The catalyst involves cinchona alkaloid derived primary amine 1, in combination with chiral phosphoric acid 2, setting the stage for a cooperative mechanism. The catalyst salt formed between 1 and one equivalent of chiral phosphoric acids, is believed to deliver a dienamine, which reacts with the benz-hydryl cation through a highly ordered transition state.