Enantioselective One-Pot Synthesis of Substituted Cyclohexenones

Significance

The authors report the enantio­selective synthesis of substituted cyclohexenones bearing an all-carbon quaternary stereocenter in the C4 position. The corresponding products were obtained in good yields and good to high enantioselectivities. Proline-derived sulfon­amide 3 catalyzed the reaction between different enones 1 and α-branched aldehydes 2 only in the presence of benzylamine. Thus, it seems likely that both carbonyl reaction partners have to be activated by means of aminocatalysis. In the proposed mechanism the benzylamine-derived enamine of 2 is reacting with the iminium ion formed from 3 and 1. An alternative mechanism could involve the attack of the 3-derived enamine of 2 to the imine formed by condensation of benzylamine and 1. Both scenarios can be supported by reasonable hydrogen-bonding interactions.