Phosphorus analogs of amino acids. IV. Syntheses of unusual 1-aminophosphonic acids via Diels-Alder reactions of diethyl (N-acyliminomethyl)phosphonates.
RN:CHP(O)(OEt)2 (R = Bz, PhSO2) react with electron-rich dienes in (4 + 2)-cycloaddns. either as dienophiles or as diene components to yield 3-(diethoxy)phosphoryl-2-azabicyclo[2.2.1]hept-5-enes I and 2-(diethoxy)phosphoryl-2,3-dihydro-4(1H)-pyridone derivs. II (R1 = R2 = H; R1R2 = bond) or R3CH:CHCOCHR4CH(NHBz)P(O)(OEt)2 (R3 = H, OMe, R4 = H; R3R4 = CH2CH2) and MeO2CCMe2CH(NHBz)P(O)(OEt)2 resp. Ene reactions of RN:CHP(O)(OEt)2 with 2-phenyl-1-propene, acetylacetone and quadricyclane afford adducts in low yield.
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