Ir-Catalyzed Selective Hydroboration of 2-Substituted 1,3-Dienes: A General Method to Access Homoallylic Boronates

An operationally simple protocol for the 4,3-selective hydroboration of 2-substituted 1,3-dienes using an iridium catalyst is described. Independently of the nature (alkyl, aryl, heteroaryl) and the size of the substituent in the 2-position, it provides access to a variety of homoallylic boronates featuring a 1,1-disubstituted olefin in high yield and chemo- and regioselectivity. An array of potentially sensitive functional groups is well-tolerated, and the method can be extend to 1,2-disubstituted 1,3-dienes. Derivatization of the homoallylic boronates is also demonstrated using contemporary catalytic and enantioselective processes.