Iridium(I)-catalyzed C-H Borylation of α,β-Unsaturated Esters with Bis(pinacolato)diboron.

A new process has been developed for the iridium(I)-catalyzed vinylic C-H borylation of α,β-unsaturated esters with bis(pinacolato)diboron (B2 pin2 ). These reactions proceeded in octane at temperatures in the range of 80-120 °C to afford the corresponding alkenylboronic compounds in high yields with excellent regio- and stereoselectivities. The presence of an aryl ester led to significant improvements in the yields of the acyclic alkenylboronates. Crossover experiments involving deuterated substrates as well as a mixture of stereoisomers confirmed that this reaction proceeds via a 1,4-addition/β-hydride elimination mechanism. Notably, this reaction was also used to develop a one-pot borylation/Suzuki-Miyaura cross-coupling procedure.