To date, only a few instances of S₄-symmetric organic molecules exist. In principle, spirobi-(dinaphthoazepin)ium cations can achieve this highly symmetric point group. Heating racemic 2,2′-bis(bromomethyl)-1,1′binaphthyl with aqueous ammonia afforded a mixture of rac- and meso-3,3′,5,5′-tetrahydro-4,4′-spirobi[dinaphtho[2,1-c:1′,2′-e]azepin]-4-ium bromide which was separated by fractional crystallisation. Both stereoisomers were characterised spectroscopically, and their crystal structures were determined and compared. The rac crystal structure differs significantly from the known enantiopure one. The meso molecules display a near-perfect S₄ symmetry. Upon treatment with KO^tBu, both isomers undergo Stevens rearrangement.

中文翻译：

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轴向-手性螺双-（萘并氮杂）鎓盐的外消旋和内消旋晶体结构：S4-对称分子的出现

迄今为止，仅存在少数S ₄对称有机分子实例。原则上，spirobi-(dinaphthoazepin)ium 阳离子可以实现这种高度对称的点群。用氨水加热外消旋 2,2'-双（溴甲基）-1,1 '联萘，得到外消旋- 和内消旋-3,3',5,5'-四氢-4,4'-螺二[二萘并[ 2,1-c:1',2'-e]azepin]-4-溴化鎓，通过分级结晶分离。两种立体异构体都进行了光谱表征，并确定并比较了它们的晶体结构。外消旋晶体结构与已知的对映体纯晶体结构显着不同。所述内消旋分子显示接近完美的小号₄对称性。KO治疗后^t Bu，两种异构体都发生史蒂文斯重排。