Essential role of phosphines in organocatalytic beta-boration reaction

The use of phosphines to assist the organocatalytic beta-boration reaction of alpha,beta-unsaturated carbonyl compounds has been demonstrated with a selected number of substrates. The new method eludes the use of Bronsted 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 B(2)pin(2) is present forming eventually the ion pair [alpha-(H),beta-(PR3)-ketone](+)-[B(2)pin(2)center dot MeO](-) that is responsible for the catalysis.