Diels-Alder reaction with phosphaalkenes. Synthesis of functionalized λ3 phosphabenzenes.

Intramolecular [4 + 2] cycloadditions involving transient phosphaalkene intermediates as dienophiles: a useful entry to phosphabicyclo[4.3.0]non-4-ene derivatives

“…Selfcondensations are usually avoided by steric or electronic effects and by complexation with a transition metal. Some cycloadditions lacking stabilisation of the P II intermediate occur in high yield, 3 especially when the cycloadducts spontaneously aromatize, thus giving a useful entry to functionalised phosphinines; 4 in most cases however the desired cycloadducts are accompanied of various amounts of self-condensed products. 2d In order to circumvent this problem we thought to trap the transient species by internal cycloaddition.…”