Copper-Catalyzed Conjugate Borylation of Enones

Key words

copper catalysis - borylation - conjugate addition - oxidation

Significance

The value of boron-containing compounds in organic synthesis has been appreciated for decades. In 2000, the Hosomi group disclosed the first copper-catalyzed borylation reaction utilizing a simple monodentate phosphine as the ligand and B₂pin₂ as the boron source. Michael acceptors, in particular enones, were used as the accepting π-system to afford the borylated products. This field has seen unceasing developments, particularly enantioselective variants, in the past two decades.

Review

Hemming et al. Chem. Soc. Rev. 2018, 47, 7477–7494.

Comment

Notably, linear and cyclic enones were tolerated, but tetrasubstituted olefins were unreactive in the transformation, an unmet challenge in the field. The authors reasoned that the role of the phosphine was to ligate the copper complex and not to activate the diboron reagent. Using excess phosphine led to inhibition of the reaction, and ³¹P NMR analysis of the phosphine with B₂pin₂ showed negligible change in the chemical shift compared to the free phosphine. Conversely, the ³¹P NMR signal of the phosphine and copper resulted in a downfield shift, suggesting coordination.

Publication History

Article published online:
18 October 2022