Synthesis of 5-alkylidene-4,5-dihydro-3H-1,2,4(λ3)-diazaphospholes from α-silyl-α-diazoketones and phosphaalkenes

Article abstract of DOI:10.1016/0040-4020(96)00541-8

5-Alkylidene-4,5-dihydro-3H-1,2,4(λ³)-diazaphospholes (II) arise from a [3+2]cycloaddition reaction between various, differently substituted phosphaalkenes and 2-siloxy-1-diazoalkenes that are present to a minor extent in a thermal equilibrium with α-silyl-α-diazoketones. The cycloaddition products 4a-g, 6a,b,e,f and 8 are sufficiently thermally stable to be isolated. In other cases, silyl group migration (ring-C → N or O → N) leads to isomeric N-silyl-1,2,4-diazaphospholes.