Ito H,
Yamanaka H,
Tateiwa J,
Hosomi A.
*
University of Tsukuba, Japan
Boration of an α,β-Enone using a Diboron Promoted by a Copper(I)–Phosphine Mixture
Catalyst.
Tetrahedron Lett. 2000;
41: 6821-6825
DOI:
10.1016/S0040-4039(00)01161-8
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.
