Dialkylethynylphosphine oxides; synthesis and reactions

Dimethyl- and dibutyl-ethynylphosphine oxide R2P(O)C ≡ CH with R = CH3 and n-C4M9, respectively, have been prepared from the corresponding dialkylphosphinic chlorides. Reactions of (C2H5)2NH, (CH3)2NH2, NaOCH3, NaOC2H5, NaSC2H5, HCl and HI with these ethynylphosphine oxides afforded 1: 1 adducts of the general formula R2P(O)CH = CHY. With the exception of alkoxide the addition occurred in the trans fashion yielding the cis compounds, but several adducts thermally rearranged to the trans isomers. As a side reaction with Na OC2H5, nucleophilic substitution at the phosphorus atom was observed. The stereochemistry of the reactions was established by NMR spectroscopy. The influence of substituents on coupling constants was studied.