Unusual borane addition to conjugated dienylphosphanes under frustrated Lewis pair conditions

Abstract

Dimesitylphosphinoisoprene 9a reacts with a series of R-B(C₆F₅)₂ boron Lewis acids by isomerization and subsequent 1,4-P/B addition to give the heterocyclic phosphonium/borate zwitterionic products 13. Subsequent hydride abstraction from the isoprenyl derived methyl group by trityl cation proceeds with elimination of the R-B(C₆F₅)₂ reagent to give the heterocyclic phosphonium system 20.