Copper(i)-catalysed regio- and diastereoselective intramolecular alkylboration of terminal allenes via allylcopper(i) isomerization.

We report the first copper(i)-catalysed intramolecular alkylboration of terminal allenes with an alkyl halide moiety. The reaction provides alkenylboronates bearing a four-membered ring structure with high regio- and diastereocontrol. A possible reaction mechanism is proposed, involving the facile isomerization of an allylcopper(i) intermediate. A DFT study explains the experimental regio- and diastereoselectivity.