Unusual borane addition to conjugated dienylphosphanes under frustrated Lewis pair conditions

摘要

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.