Dehydrogenation of the N-[2-(aminocarbonyl)phenyl]piperidines 1 -5 using Hg(II)-EDTA, generated the quinazolinones 6 -9 . Increasing size of the 4-substituent in the piperidine decreased the oxidation rate and the product yield.
N-[2-(Hydroxyiminomethyl)phenyl]piperidines 18-22 showed a different behaviour. While 18 with H g(II)-EDTA in water produced the oxime lactam 24 in quantitative yield, the 4- substituted piperidines 19-21 caused not only a lower reaction rate but also an altered product pattern. The double dehydrogenation to lactams was reduced and the cyclic nitrones, formed by two electron withdrawal, became dominant. From the spiro compounds 21 and 22, solely the quinazoline-N-oxides 29 and 30 resulted. The mechanism of the reactions is discussed.
Dehydrogenation of 2-(1-piperidinyl)-benzaldehydes 1-3 using mercury(II)-EDTA gen erated the lactams 4-6, indicating a reversible reaction of a carbinolamine intermediate with the formyl group. The yields and oxidation rates decreased by 4-substitution in the piperidine moiety.
The 2-(1-piperidinyl)-acetophenones 11, 16-19 showed a similar behavior with mercury(II)-EDTA but gave rise to a product pattern. The trans-benzoquinolizidones 12, 20, 23, 26, 29 resulted from the cyclic iminium compounds reacting with the acetyl group as nucleophile. By another oxidation these species were partially transformed to the quinolinones 13, 21, 24, 27, 30. An intermediate electrophilic neighboring of the carbonyl group with the cyclic hemiaminals led finally to the lactams 14, 22, 25, 28, 31. Mechanisms for the reactions are proposed