When 2-(2-methyl-1-piperidinyl)ethanol derivatives 3a and 3b were dehydrogenated with Hg(II)- EDTA, an iminium function involving the tertiary α-carbon atom of the piperidine ring is formed regioselectively. Cyclization of these intermediates yielded diastereomeric mixtures of oxazolidines 7a and 7b, in solutions of which hydroxy-enamine species 8a/9a and 8b/9b, respectively, could be detected by NMR spectroscopy. A hydroxy-enamine derived from 7a could be trapped by cycloaddition to tetrazine 10. Protonation of the oxazolidines generated the iminium salts 6a/6b・X with loss of a chirality center. For prevention of different directions of ring dehydrogenation in the 2-(3-methyl- 1-piperidinyl)ethanol compounds, the 6-position was blocked with two methyl groups. With amino alcohol 17, the isolation of one of the racemates in pure form was achieved, which by dehydrogenation produced a diastereoisomeric lactam mixture 18, as shown by NMR spectroscopy. Reaction of 2-(4-methyl-1-piperidinyl)ethanol 19 with Hg(II)-EDTA gave rise to a diastereomeric lactam mixture 21 in the ratio 60 : 40. From enantiomerically pure phenyloxiranes, the amino alcohols R(-)-19 and S(+)-19 became available. Their dehydrogenation under standardized conditions always showed a spreading range of isomeric lactams, which could not be separated.
当2-(2-甲基-1-哌啶基)乙醇衍生物3a和3b与Hg(II)-EDTA脱氢时,哌啶环的叔α-碳原子形成区域选择性的亚胺功能。这些中间体的环化产生了对映异构体混合物7a和7b的恶唑啉,通过NMR光谱学可以检测到溶液中的羟基烯胺物种8a/9a和8b/9b。来自7a的羟基烯胺可以通过与四嗪10的环加成反应捕获。恶唑啉的质子化生成了亚胺盐6a/6b・X,并失去了一个手性中心。为了防止2-(3-甲基-1-哌啶基)乙醇化合物中环的脱氢反应沿不同方向进行,第6位被两个甲基基团阻断。使用氨基醇17,实现了纯形式的一个对映异构体的分离,其脱氢反应生成了由NMR光谱学显示的立体异构体混合物18。2-(4-甲基-1-哌啶基)乙醇19与Hg(II)-EDTA反应产生对映异构体混合物21的比例为60:40。从对映体纯的苯基环氧烷获得了氨基醇R(-)-19和S(+)-19。在标准化条件下它们的脱氢反应总是显示出不能分离的异构内酰胺的广泛范围。