Diastereo- and Enantioselective anti-Alkoxyallylation Employing Allylic gem-Dicarboxylates as Allyl Donors via Iridium-Catalyzed Transfer Hydrogenation

摘要

Enantioselective carbonyl allylation represents an important class of C-C bond-forming reactions that have found broad use in organic synthesis. Among allylation protocols, enantioselective aldehyde α-alkoxyallylation provides an efficient means of generating allylic vicinal diol substructures. To date, asymmetric syn-additions of this type have employed chirally modified alkoxy-substituted allylmetal reagents based on boron, aluminum, titanium, indium, or tin. Indirect enantioselective aldehyde α-alkoxyallylation can be achieved using chirally modified reagents that promote aldehyde α-silylallylation or α-borylallylation followed by oxidation of the C-Si or C-B bond, respectively. For direct methods, stereocontrolled access to anti-alkoxyallylation products is problematic because of difficulties encountered in the synthesis of the requisite E-configured allylmetal reagents. This fact has motivated alternate approaches to the anti-1 -ene-2,3-diol functional group array.