Reactions of 3-carbomethoxy-2-aza-1,3-butadiene derivatives with dienophiles

Abstract

The reactions of 1,1-diphenyl-3-carbomethoxy-2-aza-1,3-butadiene derivatives la- e (on C4 : H,H or H,CH 3 or H,C 6H 5, both E and Z isomers), and of the C4 unsubstituted 1 -phenyl-1-ethoxy analogue 2, were studied with a number of electron-rich and electron-poor dienophiles, with results showing that la- e give heterocycloadducts in Diels-Alder reactions with electron-poor dienophiles. Michael adducts were obtained from the EtAlCl 2 catalyzed reactions of these compounds with dimethyl acetylendicarboxylate. Compound 2 gave heterocyclic adducts as well but behaved like a nucleophile, at least in the case of the reactions with dimethyl acetylendicarboxylate and ethyl propynoate: these reactions afforded 2-azatrienes as Michael adducts that gave pyridine derivatives upon heating. The synthesis of the new 1-ethoxy-2-aza-1,3-butadiene 2 is also reported.