SYNTHESIS AND REACTIVITY OF CYCLIC 6-MEMBERED 6-PI-MEMBERED AND 4-MEMBERED 4-PI-ELECTRON YLIDES

N-Phosphinonitrilimine 1 and phosphine azides 4 react with dimethyl ac etylenedicarboxylate via formal [4 + 2] cycloadditions affording 1,2,3 lambda(5)-diazaphosphinine 2 (90% yield) and 1,2,3,4 lambda(5)-triaza phosphinines 5 (63-75% yield), respectively. Although 2 is reluctant t oward dinitrogen extrusion, derivatives 5 afford 1,2 lambda(5)-azaphos phetes 6 (80-90% yield) by heating in refluxing toluene. Four-pi-elect ron four-membered rings 6 react via the ring nitrogen atom with a vari ety of electrophiles. The four-membered ring structure is preserved by addition of boron trifluoride or iodomethane, while ring-opening reac tions are observed with water, pentafluorobenzonitrile, and carbon dis ulfide; ring expansion reactions occurred with dimethyl acetylenedicar boxylate, methyl isothiocyanate, phenyl isocyanate, trimethylsilyl iso cyanate, and isothiocyanate.