Sterically congested boronate and silane synthesis via electronically controlled protoboration and protosilylation

Multi-functionalized tertiary/secondary boronates and silanes have found wide applications in areas spanning organic synthesis, advanced material development, and pharmaceutical research. Effective access to these versatile motifs via protoboration/silylation of allenes remains unfulfilled. Capitalizing on the fluorine effects, here we report copper-catalyzed protoboration/silylation of gem-difluoroallenes, which shows an abnormal reactivity profile. In stark contrast to the conventional paradigms of allene functionalization reactions, which are often subjected to the steric-control mode for more facile reaction initiation on lower-substituted double bonds, the present reaction displays a virtually reversed regioselectivity for the more sterically congested pi system. The synergistic LUMO-lowering perturbation and stabilization of nascent organo-copper by fluorine substituents are deemed critical for guaranteeing the high fidelity of the present transformation. We not only apply this developed methodology to the late-stage modification of compounds derived from natural products but also highlight the utility of the obtained gem-difluoroalkenes in further synthetic elaborations.