(, 2, 2-Dimethylpropylidync) phosphane (7) undergoes regiospecitic [3+ 2]-cycloaddition reactions with the arylnitrile oxides 2a—c to yield the 1, 2, 4-oxazaphospholes 8a—c. In the reaction of phosphaalkyne 7 with 2, 2-dimethylpropancnitrile oxide (Zd) the 1: 2-adduct. I0 is formed in addition to 8d. The reaction of 7 with the nitrile sulphide 12 produces the 1, 2, 4- thiazaphospholc 13. The 1H-l, 2, 4-diazaphospholcs I8a—c are obtained from the ...