Making Use of the Functional Group Combination of a Phosphane/Borane Lewis Pair Connected by an Unsaturated Four-Carbon Bridge

Abstract

Unsaturated, C4-bridged, tBu2P/B(C6F5)2-containing phosphane/borane Lewis pair 6a reacts with 2-methylbutenyne in a two-step reaction sequence of allylboration followed by addition of the P/B frustrated Lewis pair (FLP) to the resulting vinyl group to give the zwitterionic heterobicyclic product 14. The P/B pair 6b (–PMes2) reacts with the conjugated ynone 15 in a similar way by means of allyl-B transfer to the ketone to eventually give the bicycle 17. Compound 6b undergoes 1,4-P/B FLP addition to methyl vinyl ketone, and it adds to an imine or a nitrile by B-allyl transfer. Compound 6a reacts with the persistent TEMPO radical by addition to the boron Lewis acid followed by H-atom transfer from the allylic substituent to nitrogen. The reaction sequence is closed by H abstraction by a second equivalent of TEMPO to yield the tBu2P-CH2-substituted dienyl-B(C6F5)2-OTMP(H) product 34.