Quinazoline derivatives by cyclodehydrogenation of N-(2-substituted aryl)-piperidines

Dehydrogenation of the N[2(aminocarbonyl)phenyl]piperidines 1-5 using Hg(II )-EDTA, generated the quinazolinones 6-9. Increasing size of the 4-substitu ent in the piperidine decreased the oxidation rate and the product yield. N-[2-(Hydroxyiminomethyl)phenyl]piperidines 18-22 showed a different behavi our. While 18 with Hg(II)-EDTA in water produced the oxime lactam 24:in qua ntitative yield, the 4-substituted piperidines 19-21 caused not only a lowe r reaction rate but also an altered product pattern. The double dehydrogena tion to lactams was reduced and the cyclic nitrones, formed by two electron withdrawal, became dominant. From the spiro compounds 21 and 22, solely th e quinazoline-N-oxides 29 and 30 resulted. The mechanism of the reactions i s discussed.