The use of phosphines to assist the organocatalytic β-boration reaction of α,β-unsaturated carbonyl compounds has been demonstrated with a selected number of substrates. The new method eludes the use of Brönsted bases to promote the catalytic active species and PR3 becomes essential to interact with the substrate resulting in the formation of a zwitterionic phosphonium enolate. This species can further deprotonate MeOH when B2pin2 is present forming eventually the ion pair [α-(H),β-(PR3)-ketone]+[B2pin2·MeO]– that is responsible for the catalysis.
Essential role of phosphines in organocatalytic β-boration reaction
Org. Biomol. Chem. 2012, 10, 9677-9682.