Molecular Design of New Optically Active Sensitizers for Highly Efficient Photosensitized Asymmetric Reactions

在本研究中，我们首先研究了几种天然光学活性醇芳酸酯敏化的前手性环烯和环丙烷的对映异构化反应，给出了光学产率(o.y)。高达40%。为了提高S的合成质量，我们通过分子力学和分子轨道计算，设计了一系列新型的手性增敏剂，它们携带大量和/或给电子取代基。这些量身定做的光敏剂提供了非常高的对映分化光敏剂，在室温下O.YS；50%(r.t.)以上令人鼓舞的结果促使我们研究了光化学中更困难、更没有尝试过的领域：对映异构光加成反应。在-90ﾟ下，这一比例高达70%。因此，手性萘(二)羧酸盐敏化的1，1-二苯基丙烯与反马尔可夫尼科夫甲醇对映体的不对称反应，即使在反应温度下也能得到高达27%的对映S。本工作清楚地表明，光敏化对映异构单分子和双分子反应在不对称合成中不仅具有理论意义，而且具有重要的实用价值。

In the present study, we first examined the enantiodifferentiating photoisomerizations of prochiral cycloalkenes and cyclopropanes sensitized by several aromatic esters of naturally occurring optically active alcohols to give the optical yields (o.y.) of up to 40%. In order to enhance the product s o.y., we designed a variety of novel chiral sensitizers carrying bulky and/or electron-donating substituents with the aid of molecular mechanics and molecular orbital calculations. These tailored photosensitizers afforded exceptionally high, as enantiodifferentiating photosensitizations, o. y. s. of >50% at room temperature (r. t.) and of up to 70% at -90ﾟCThe above encouraging results prompted us to investigate the more difficult, never tried area of photochemistry : enantiodifferentiating photoaddition reactions. Thus, the enantiodifferentiating anti-Markovnikov methanol addition to 1,1-diphenylpropene sensitized by chiral naphthalene(di) carboxylates gave the o. y. s up to 27% even at r. t.The present work clearly indicates that the photosensitized enantiodifferentiating uni- and bimolecular reactions, demanding only a catalytic amount of chiral sensitizer, are not only of theoretical interest but also of practical importance in the asymmetric synthesis.