Development of Multicomponent Reactions Proceeding via π-Bond-triggered Metallate Rearrangement

Alkylboronic esters are versatile, stereochemically rich building blocks, and numerous methods have been developed to access them. Among these, the 1,2-metallate rearrangement of vinylboronates has emerged as a powerful approach to 1,2-difunctionalize a vinyl group, furnishing complex alkylboron frameworks from simple starting materials. When carbon electrophiles are used, two new C-C bonds form in a single operation, enabling rapid assembly of highly functionalized products. To broaden the electrophile class, we proposed that highly reactive π-electrophiles could initiate the rearrangement and, at the same time, generate an anionic species for the next bond-forming event via π-bond cleavage. Guided by this idea, we developed (i) an aryne-triggered annulation and (ii) a ketene-triggered multicomponent coupling of simple vinylboronates. The strain of arynes and the polarized heterocumulene character of ketenes allow them to activate vinylboronates, trigger 1,2-metallate migration, and generate anionic intermediates that are trapped intramolecularly by a neighboring boronic ester or intermolecularly by external electrophiles. Here we describe the development, scope, limitations, and mechanistic features of these transformations.