Unusually Coordinated Phosphorus Compounds; 7¹. Adamant-1-ylmethylidynephosphine, A New, Stable Phosphaalkyne

The reaction of tris[trimethylsilyl]phosphine (4a) as well as of the lithium bis[trimethylsilyl]phosphide·; tetrahydrofuran complex (4b) with 1-adamantoyl chloride (5) results in the formation of the phosphaalkene 7 in 67% or 96% yield, respectively. Subsequent sodium hydroxide or tetra-n-butylammonium fluoride-catalysed elimination of hexamethyldisiloxane from 7 at 20/90 °C gives rise to the phosphaalkyne 8 in 83 or 71% yield. The phosphaalkyne 8 undergoes smooth [3 + 2]cycloaddition reactions with 1,3-dipoles such as the nitrile oxide 9, the diazo compounds 12a-c, and the azide 15 to produce the phospholes 11,14a-c, and 16, respectively. The phosphaalkene 7 reacts with the dipoles 9 and 12a to give the same cycloadducts 11 and 14a, respectively. In these two reactions, the primary adducts undergo spontaneous (10 → 11) or sodium hydroxide-catalysed (13 → 14a) elimination of hexamethyldisiloxane.