Condensation of 2-alkoxypropenals with N,N- and N,O-1,2-binucleophiles. A route to 2-(1'-alkoxyvinyl)imidazo-lidines and -oxazolidines

Condensation of 2-ethoxypropenal with diaminoethylene in different solvents (CHCl₃, MeCN, H₂O, DMSO) at room temperature gives an equilibrium mixture (1:1-1.5) of tautomeric 2-(1'-ethoxyvinyl)-1,3-imidazolidine and 2-aminoethylimine of 2-ethoxypropenal as well as 1,2-bis(2'-ethoxypropenyl-ideneamino)ethylene. The latter is readily prepared in quantitative yield using a twofold excess of the aldehyde. ¹H NMR was used to demonstrate the effect of heating on the dynamics of the ring-chain tautomeric equilibrium. Reaction of the 2-alkoxypropenals with N-methyl- and N,N'-diphenyl-1,2-diaminoethylenes and with N-phenylaminoethanol gives only the corresponding substituted imidazolidines in 43-95% yield.