Sulfonylation of Cyclic Allylborates with DABSO: Synthesis of Allylic Sulfones Having an Allylic Boronate Moiety.

A three-component coupling reaction for the synthesis of highly substituted allylic sulfones bearing an allylic boronate moiety is described. This method uses cyclic allylborates, a sulfur dioxide surrogate (DABSO), and organic halides such as alkyl halides and allylic bromides. The reaction proceeds with high α-selectivity, which is notable since γ-selective functionalization is more common for allylic boron compounds. The reaction demonstrates a broad substrate scope with respect to both the cyclic allylborates and organic halides. Mechanistic investigations suggest that the reaction proceeds via the initial formation of a γ-functionalized SO2 intermediate, followed by a rearrangement to afford the final α-product.