Copper-Catalyzed Regioselective Formation of Tri- and Tetrasubstituted Vinylboronates in Air

• Published in: ACS catalysis Vol. 4; no. 5; pp. 1564 - 1569
• Main Authors: Bidal, Yannick D, Lazreg, Faïma, Cazin, Catherine S. J
• Format: Journal Article
• Language: English
• Published: American Chemical Society 02.05.2014
• Subjects: carboboration; copper; hydroboration; alkynes; N-heterocyclic carbenes
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/cs500130y

The first “in air” copper-catalyzed method for the selective synthesis of tri- and tetrasubstituted vinylboronate derivatives is presented. Three different variants of the borylation of internal alkynes (α-hydroboration, β-hydroboration, and carboboration) are described using a single catalyst: [Cu­(Cl)­(IMes)] (IMes = N,N′-bis-[2,4,6-(trimethyl)­phenyl]­imidazol-2-ylidene) without taking any precaution to avoid the presence of air. Bis­(pinacolato)­diboron was used to afford β-hydroborated products in the presence of methanol. Adding instead another electrophile allowed the formation of tetrasubstituted vinylboronate species. Finally, the α-products were obtained using pinacolborane as the boron source. All compounds were obtained in high yield with excellent regioselectivity at low catalyst loading (0.04–2 mol %). The protocol constitutes a very convenient route to access these highly valuable molecules.