Synthesis of gem-difluoromethylenated analogues of boronolide.

The straightforward synthesis of four gem-difluoromethylenated analogues 4-7 of boronolide is described. The key steps of the synthesis include the concise preparation of the key intermediates 12a-b through the indium-mediated gem-difluoropropargylation of aldehyde 9 with the fluorine-containing building block 11 and the efficient construction of alpha,beta-unsaturated-delta-lactones 15a-b via BAIB/TEMPO-procedure.