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

• Published in: Chemistry, an Asian journal an Asian journal, 2016-05, Vol.11 (9), p.1400-1405
• Main Authors: Sasaki, Ikuo, Taguchi, Jumpei, Doi, Hana, Ito, Hajime, Ishiyama, Tatsuo
• Format: Article
• Language: English
• Subjects: alkenyl boronates; borylation; diboron; iridium; α,β-unsaturated esters; β-unsaturated esters
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201600078

A new process has been developed for the iridium(I)‐catalyzed vinylic C−H borylation of α,β‐unsaturated esters with bis(pinacolato)diboron (B2pin2). 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. A lucky strike with B2pin2: A new method has been developed for the vinylic C−H borylation of α,β‐unsaturated esters with bis(pinacolato)diboron (B2pin2) using iridium(I) catalysts. These reactions proceeded in octane at 80–120 °C to afford the alkenylboronic compounds in high yields with excellent regio‐ and stereoselectivities.