Boraformylation and Silaformylation of Allenes

The boraformylation of allenes with B2(pin)2 and a formate ester as boron and formyl source, respectively, proceeds in the presence of a copper catalyst. The reaction selectively affords the corresponding β‐boryl β,γ‐unsaturated aldehydes in good to high yields. Furthermore, the silaformylation of allenes was achieved with a formate ester and PhMe2Si−B(pin) as the silicon source. Boron or silicon? Boraformylation and silaformylation reactions of allenes with formate esters smoothly proceed in the presence of a copper catalyst using B2(pin)2 and PhMe2Si−B(pin) as the boron and silicon source, respectively. These reactions selectively afford the corresponding β‐boryl and β‐silyl β,γ‐unsaturated aldehydes in good to high yields with excellent regioselectivity.