Chemical behaviour of a prototype boryl(phosphino)carbene

Abstract

We recently disclosed the synthesis of a novel "push-pull" boryl(phosphino)carbene. To determine the influence of this substitution pattern on the chemical behaviour, a study into the reactivity of the prototype (1) of this new family of B(sp(2))-substituted phosphinocarbenes was undertaken. Carbene 1 exhibits one of the most common intramolecular rearrangements of singlet carbenes, involving a 1,2-mesityl shift, and typical [2+1] cycloaddition reactions with electron-poor acrylonitrile. A pronounced α,β-ambiphilic character was also shown by the reaction of 1 with benzaldehyde, leading to phosphorylalkene 4. Due to its specific electronic properties, carbene 1 also exhibits unprecedented reactivity with chloroacrylonitrile, enabling the formation of bicyclo[1.1.0]phosphetanium salt 6 and borylcyclopropene 9, which have been fully characterised by NMR spectroscopy and X-ray crystallography.

Keywords: Wittig reactions; boron; borylcyclopropenes; carbenes; cycloaddition; phosphiranium.