A practical diastereoselective reduction of spiroisoimidazole to afford rac‐1,2‐diarylethylenediamines was developed. Zinc was used as a reducing agent in a mixture of basic H₂O and an alcoholic cosolvent under open air. The choices of NaOH as the base and MeOH as the cosolvent were key factors that heightened selectivity, and under these optimized conditions, the yield of rac‐1,2‐diphenylethylenediamine (DPEN) was > 11‐fold that of meso isomer. The reaction was amenable to a 0.10 mol scale, which resulted in the isolation of 16.9 g of rac‐DPEN. Control experiments suggested that the reduction with zinc followed a different pathway from that of a known Birch reduction.

中文翻译：

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在NaOH水溶液中用锌粉进行非对映选择性还原。和MeOH用于合成（±）-1,2-二芳基乙二胺

开发了一种实用的非对映选择性还原螺异咪唑以提供rac 1,2-二芳基乙二胺的方法。锌在露天条件下用作碱性H ₂ O和含醇助溶剂的混合物中的还原剂。NaOH作为碱的选择以及MeOH作为助溶剂的选择是提高选择性的关键因素，在这些优化的条件下，rac 1,2-二苯基乙二胺（DPEN）的收率是内消旋异构体的11倍以上。反应适合于0.10 mol规模，从而分离出16.9 g rac -DPEN。对照实验表明，锌的还原与已知的桦木还原的还原途径不同。