Interaction of barbituric acids with o-dialkylaminobenzaldehydes

Barbituric or 2-thiobarbituric acids interact with o-dialkylaminobenzaldehydes to give 5-o-dialkylaminobenzylidene derivatives, which cyclise into 2,4,6-trioxoperhydropyrimidine-5-spiro-3′-(1′,2′,3′,4′-tetrahydroquinolines) under mild conditions; the mechanism of the key stage of a tert-amino effect reaction is disclosed on the basis of the XRD analysis of 1,3-dimethyl-5-(2-dimethylamino-4-nitrobenzylidene)barbituric acid.