Journal of Organic Chemistry vol:70 issue:1 pages:191-198
1,4- And 1,2-Addn. of sodium malonate to 2-aza-1,3-butadienylphosphonate gave 2-aza-3-buten-1-ylidenemalonate or 2-azaallylphosphonate, in dependence of the substituent in α-position; 3-carboxy-2-oxo-1-pyrrolidinylphosphonates were prepd. by cyclization of the addn. products. Reaction of R12C:CHN:CHPO(OEt)2 (1a-c) with NaCH(CO2Me)2 gave R12C:CHNHCH:C(CO2Me)2 [12a-c; R1 = Me, Et, or R12 = (CH2)5], as a result of 1,2-addn. and elimination of the phosphonate moiety. Phosphonoazabutadienes, having aryl substituent in α-position, undergo 1,4-addn. of NaCH(CO2Me)2, affording (MeO2C)2CHCR12CH:NCH(Ar)PO(OEt)2 (21-26, R1 = Me, Ar = 2-, 3- or 4-halophenyl). Imines 21-24 were cyclized under hydrogenation conditions, giving aryl[4,4-dimethyl-3-(methoxycarbonyl)-2-oxo-1-pyrrolidinyl]methylphosphonates (33-37; aryl = XC6H4, where X = 4-Br, 2-Br, 2-Cl, 4-F, 2-F). The regioselectivity of the addn. is explained by reversal of polarization of the azadiene due to the electron-withdrawing character of the halogenated Ph substituents.