An Oxyboration Route to a Single Regioisomer of Borylated Dihydrofurans and Isochromenes.

An oxyboration reaction that employs B-O σ bonds as addition partners to C-C π bonds to form borylated dihydrofurans and isochromenes has been developed. By nature of the mechanism, the reaction produces exclusively one borylated regioisomer, in contrast to and/or complementary to alternative routes that produce these borylated heterocycles via C-H activation. Access to the borylative heterocyclization route is demonstrated from alcohols directly or from a hydroboration-oxyboration sequence starting from the corresponding ketone, forming the heterocyclic core and installing the boron in one synthetic step. Catechol boronates were directly used as coupling partners in the in situ Suzuki cross-coupling reactions without transesterification to pinacol boronates.