Synthesis of Chiral gem-Difluoromethylene Compounds by Enantioselective Ethoxycarbonyldifluoromethylation of MBH Fluorides via Silicon-Assisted C-F Bond Activation.

The enantioselective ethoxycarbonyldifluoromethylation of Morita-Baylis-Hillman (MBH) fluorides with Me3SiCF2CO2Et under organocatalysis is described. Moderately functionalized chiral gem-difluoromethylene compounds with a stereogenic "C-CF2-C*" unit were synthesized in high yields with high enantioselectivities. The initial C-F bond activation is assisted by the silicon atom via a dual SN2'-SN2' stepwise pathway. Dynamic kinetic resolution of the MBH-fluorides explained the high yields and high ee's of the products. The method was extended to the enantioselective introduction of "Het-CF2" units.