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 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.