Reactions of the N-aryl(diphenylphosphanyl)aminosilane Ph2PN(Ar)SiCl3–nMen (Ar = 2,4,6-Me3C6H2, n = 0 (1a), 1 (2a), 2 (3a), 3 (4a); Ar = 2,6-iPr2C6H3, n = 0 (1b), 1 (2b), 2 (3b), 3 (4b)) with methyl propiolate and dimethyl acetylenedicarboxylate (DMAD) give two types of products, the zwitterionic heterocycles [Ph2PN(2,4,6-Me3C6H2)SiCl3](HC═CCO2Me) (5c) and [Ph2PN(Ar)SiCl3–nMen](MeO2CC═CCO2Me) (Ar = 2,4,6-Me3C6H2, n = 0 (5a), 1 (6a), 2 (7a); Ar = 2,6-iPr2C6H3, n = 0 (5b), 1 (6b), 2 (7b)) and (Z)-silyliminophosphoranylalkene ArN═P(Ph2)C(CO2Me)═C(CO2Me)SiMe3 (Ar = 2,4,6-Me3C6H2 (8a), 2,6-iPr2C6H3 (8b)). The reaction of Ph2PN(SiMe3)2 with DMAD gives only the acyclic alkene Me3SiN═P(Ph2)(MeO2C)C═C(CO2Me)SiMe3 (9), which is similar to 8a,b. In these reactions, compounds 1a–4a and 1b–4b behave as N-geminal P/Si-based Lewis pairs, which undergo a dipolar cycloaddition reaction with the alkyne. The theoretical calculations indicate that the reactions proceed through a concerted cycloaddition reaction mechanism. Th...