Many optically active 2-azaspirocyclic structures have frequently been found in biologically active natural products. In particular, Nitraria alkaloids, (+)-nitramine, (+)-isonitramine, (−)-isonitramine, and (−)-sibirine, have stereogenicity on their quaternary carbon of the 2-azaspiro[5,5]undecane-7-ol structure. To synthesize Nitraria alkaloids, we developed a new enantioselective synthetic method for chiral α-quaternary lactams via the α-alkylation of α-tert-butoxycarbonyl lactams. α-Alkylation of α-tert-butoxycarboxylactams in the circumstances of phase-transfer catalytic (PTC) system (solid KOH, toluene, and −40 °C) by virtue of the catalytic action of (S,S)-NAS bromide (5 mol %) furnished the corresponding α-alkyl-α-tert-butoxycarbonyl lactams in very high chemical (<99%) and enantioselectivity (<98% ee). Our catalytic methodology was successfully applied for the enantioselective total synthesis of Nitraria alkaloids. (+)-Isonitramine was obtained in 12 steps (98% ee, 43% yield) from δ-valerolactam through enantioselective phase-transfer catalytic allylation, Dieckmann condensation, and diastereoselective reduction as the key reactions. (−)-Sibirine and (+)-nitramine were prepared from (−)-isonitramine or its intermediate. Switching the phase-transfer catalyst from (S,S)-NAS bromide to (R,R)-NAS bromide afforded (−)-isonitramine (98% ee, 41% yield). (−)-Sibirine was synthesized by N-ethoxycarbonylation of (−)-isonitramine followed by reduction (98% ee, 14 steps, 32% yield). Furthermore, the diastereoselective reduction of (R)-2-benzhydryl-2-azaspiro[5.5]undecane-1,7-dione [(R)-15] followed by reductive removal of the diphenylmethyl group successfully gave (+)-nitramine (98% ee, 11 steps, 40% yield).

中文翻译：

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对硝基生物碱的对映选择性全合成：α-羧基内酰胺的不对称相转移催化α-烯丙基化的（+）-硝胺，（+）-艾尼曲明，（-）-艾尼曲明和（-）-西比林

在生物活性的天然产物中经常发现许多旋光的2-氮杂螺环结构。尤其是，Nitraria生物碱，（+）-硝胺，（+）-异烟酰胺，（-）-异烟酰胺和（-）-西比林碱在其2-azaspiro [5,5]十一烷-7的季碳上具有立体异构性。 -ol结构。为了合成Nitraria生物碱，我们通过α-叔丁氧羰基内酰胺的α-烷基化开发了一种新的对映选择性合成方法，用于手性α-季内酰胺。α-α-烷基化叔-butoxycarboxylactams在相转移催化（PTC）系统的情况（固体KOH，甲苯，-40℃）凭借（催化作用的小号，小号）-NAS溴化物（5 mol％）以非常高的化学性质（<99％）和对映选择性（<98％ee）提供了相应的α-烷基-α-叔丁氧羰基内酰胺。我们的催化方法已成功地用于白背生物碱的对映选择性全合成。通过对映选择性相转移催化烯丙基化，Dieckmann缩合和非对映选择性还原作为关键反应，从δ-戊内酰胺分12步（98％ee，43％收率）获得（+）-艾尼曲明。（-）-西比林和（+）-硝胺由（-）-异硝胺或其中间体制备。将相转移催化剂从（S，S）-NAS溴化物转换为（R，R）-NAS溴化物提供（-）-异烟酰胺（98％ee，41％产率）。（-）-Sibirine是通过（-）-异硝胺的N-乙氧羰基化反应，然后还原反应合成的（98％ee，14步，收率32％）。此外，（R）-2-苯甲酰基-2-氮杂螺[5.5]十一烷-1,7-二酮[（R）-15 ]的非对映选择性还原，然后还原性去除二苯甲基，成功得到（+）-硝胺（ ee：98％，11步，收率40％）。