Dialkylethynylphosphine oxides; synthesis and reactions

Dimethyl‐ and dibutyl‐ethynylphosphine oxide R 2 P(O)C ≡ CH with R = CH 3 and n ‐C 4 M 9 , respectively, have been prepared from the corresponding dialkylphosphinic chlorides. Reactions of (C 2 H 5 ) 2 NH, (CH 3 ) 2 NH 2 , NaOCH 3 , NaOC 2 H 5 , NaSC 2 H 5 , HCl and HI with these ethynylphosphine oxides afforded 1: 1 adducts of the general formula R 2 P(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 OC 2 H 5 , 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.