Direct amino acid-catalyzed cascade biomimetic reductive alkylations: application to the asymmetric synthesis of Hajos-Parrish ketone analogues.

A direct amino acid-catalyzed chemo- and enantioselective process for the double cascade synthesis of highly substituted 2-alkyl-cyclopentane-1,3-diones, 2-alkyl-3-methoxy-cyclopent-2-enones and Hajos-Parrish (H-P) ketone analogs is presented via reductive alkylation chemistry. For the first time, we have developed a single-step alkylation of cyclopentane-1,3-dione with aldehydes/ketones and a Hantzsch ester through an organocatalytic reductive alkylation strategy. A direct combination of amino acid-catalyzed cascade olefination-hydrogenation and cascade Robinson annulations of cyclopentane-1,3-dione, aldehydes/ketones, a Hantzsch ester and methyl vinyl ketone furnished the highly functionalized H-P ketone analogues in good to high yields and with excellent enantioselectivities. Many of the reductive alkylation products have shown direct applications in pharmaceutical chemistry.