Essential role of phosphines in organocatalytic β-boration reaction.

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 PR(3) becomes essential to interact with the substrate resulting in the formation of a zwitterionic phosphonium enolate. This species can further deprotonate MeOH when B(2)pin(2) is present forming eventually the ion pair [α-(H),β-(PR(3))-ketone](+)[B(2)pin(2)·MeO](-) that is responsible for the catalysis.