Stannyl phosphaketene as a synthon for phosphorus analogues of β-lactams

The reaction of the stannyl phosphaketene (Nacnac)SnPCO 1 (Nacnac = CH{(CMe)(2,6-ⁱPr₂C₆H₃N)}₂) with B(C₆F₅)₃ produced the 1,4-addition product of (Nacnac)SnPCO(B(C₆F₅)₃). However, the corresponding reactions in the presence of dimethyl maleate, diisopropyl fumarate or diethyl-but-2-ynedioate gave [2+2] addition yielding four-membered phosphacycles, ((Nacnac)Sn(MeO₂C))CHPC(OB(C₆F₅)₃)CH(CO₂Me), [(C₆F₅)₃B)PC(OSn)C(CO₂Me)CH(CO₂Me)]₂, (Nacnac)Sn(ⁱPrO₂C)CC(OAl(C₆F₅)₃)P[CH(CO₂ⁱPr)CH₂(CO₂ⁱPr)]CH(CO₂ⁱPr), and (Nacnac)SnP (EtO₂CCC(CO₂Et))CO(B(C₆F₅)₃), respectively. In contrast, the corresponding reaction of phenylacetylene gave the FLP-addition product (Nacnac)SnOC(P)C(Ph)CH(B(C₆F₅)₃). Collectively, this reactivity demonstrates that the stannyl phosphaketene 1 can act as a synthon for P-analogues of β-lactam derivatives.