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- i Pr 2 C 6 H 3 N)} 2 ) with B(C 6 F 5 ) 3 produced the 1,4-addition product of (Nacnac)SnPCO(B(C 6 F 5 ) 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(MeO 2 C))CHPC(OB(C 6 F 5 ) 3 )CH(CO 2 Me), [(C 6 F 5 ) 3 B)PC(OSn)C(CO 2 Me)CH(CO 2 Me)] 2 , (Nacnac)Sn( i PrO 2 C)CC(OAl(C 6 F 5 ) 3 )P[CH(CO 2 i Pr)CH 2 (CO 2 i Pr)]CH(CO 2 i Pr), and (Nacnac)SnP (EtO 2 CCC(CO 2 Et))CO(B(C 6 F 5 ) 3 ), respectively. In contrast, the corresponding reaction of phenylacetylene gave the FLP-addition product (Nacnac)SnOC(P)C(Ph)CH(B(C 6 F 5 ) 3 ). Collectively, this reactivity demonstrates that the stannyl phosphaketene 1 can act as a synthon for P-analogues of β-lactam derivatives.