Quinolizidines, mercuric acetate oxidation

The mechanistic sequence as outlined for quinolizidine-10-c/has metallic mercury as the reduced species. Mercurous acetate is the form in which the mercury eventually appears. It has been shown (76) that under the standard operating conditions, mercuric acetate will oxidize metallic mercury to the... 

In 1955, Leonard described a general method for the oxidation of cyclic tertiary amines to give enamines. Quinolizidine was dehydrogenated using mercuric acetate in 5 % aqueous acetic acid by heating on the steam bath for hr to give 92% mercurous acetate and 60% dehydroquinolizidine. 

Treatment of perhydro-4-azaazulene (3) with mercuric acetate produces a mixture of dehydro derivatives 31a and 31b, which, with acids, yields homogeneous salts of structure 32 (56JOC344). The enamine 34, which was obtained by the same route from 33, served as a model compound in a study of the synthesis of cephalotaxine (72JOC3691). A reaction with ethyl y-bromo-acetoacetate surprisingly yielded the quinolizidine 36, which was formed by rearrangement of the intermediate annellation product 35 (Scheme 3) Phthalimides 38 were obtained from a Baeyer-Villiger oxidation of 4-azaazulen-3-ones 37 (77JOC1093). 

Double bonds between carbon and nitrogen in secondary and tertiary cyclic amines are formed on treatment with mercuric acetate [401, 402, 1091], silver oxide [375], or tert-butyl hypochlorite [707]. tert-Butyl hypochlorite converts methyl pyrrolidine-2-carboxylate into methyl 1-pyrrol ine-2-carboxylate in 71% yield [707], and mercuric acetate transforms 2-terr-butylpiperidine into 2-tm-butyl-l-piperideine in 75% yield [1091]. Tertiary cyclic amines are dehydrogenated by mercuric acetate via quaternary salts [401,402]. l-Methyl-2-ethylpiperidine yields ultimately 1-methyl-2-ethyl-2-piperideine [402] and quinolizidine A -dehydroquin-olizidine [401] (equation 34). 

Dehydrogenation of tertiary amines. Leonard found that cyclic tertiary amines can be oxidized to enamines with 4 mole equivalents of mercuric acetate in 5% aqueous acetic acid at steam-bath temperature. When quinolizidine was treated in... 

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