Behaviour of Salicylaldehyde and Some of Its Derivatives in the Biginelli Reaction for the Preparation of Aryl Tetrahydropyrimidines

Sali cylald ehyde and some of it s derivat ives react with ur ea (or thi oure a) and ethyl acetoacetate (the Big inelli reaction) to give pr oduct s th at depend on the typ e of the su bstituent in the ort ho-posit ion to t he hydro xyl grou p. Alde hydes having oxygen-b ea ring subst it uents oriho to t he hyd roxyl grou p (e.g., OC H3 , N0 2 , COO H) undergo chelat ion with th e hydroxyl pro ton and lead to 4-aryl- 6-methyl-4- aryl-2oxo-l ,2,3,4- tet rahydrop yrimidine-5-ethyl carboxylate (t he class ical Biginelli pro du ct) . Compounds not having such a pr op erty give oxacyclic products formed by ad diti on of t he hyd roxyl proton to t he C5-C6 double bo nd of t he py rimid ine r ing. This study also includes compo unds having an ami no group instead of th e hyd roxyl one.