Facile synthesis of luminescent benzo-1,2-dihydrophosphinines from a phosphaalkene

The addition of 4-trifluoromethyl-1-ethynylbenzene, phenylacetylene, or 4-ethynylanisole to P-mesityldiphenylmethylenephosphine, 1, produced photoluminescent 1,2-dihydrophosphinines 4a-c, respectively, in quantitative yield via a [4 + 2] cycloaddition. Limited reactivity was observed between 1 and non-aromatic alkynes. P-[Bis(trimethylsilyl)amino][(trimethylsilyl)methylene]phosphine, 2, and P-mesityl[(t-butyl)(trimethylsiloxy)methylene]phosphine, 3, showed extremely limited reactivity with all alkynes examined. The reactivity of phosphaalkenes toward terminal alkynes is compared to that of alkenes as well as silenes and germenes.