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.