Saunthwal Rakesh K, Mortimer James, Orr-Ewing Andrew J, Clayden Jonathan
School of Chemistry, University of Bristol Cantock's Close Bristol BS8 1TS UK
Chem Sci. 2022 Jan 25;13(7):2079-2085. doi: 10.1039/d1sc06684f. eCollection 2022 Feb 16.
Enantioenriched seven-membered carbocycles are motifs in many molecules of structural and biological interest. We report a simple, practical, transition metal-free and mechanistically unusual method for the enantioselective synthesis of substituted cycloheptatrienes. By forming a coloured enolate with an appropriate absorption band and selectively irradiating , we to initiate a tandem, asymmetric anionic and photochemical ring expansion of readily accessible -benzylbenzamides. The cascade of reactions leading to the products entails enantioselective benzylic deprotonation with a chiral lithium amide, dearomatizing cyclization of the resulting configurationally defined organolithium to give an extended amide enolate, and photochemically induced formal [1,7]-sigmatropic rearrangement and 6π-electrocyclic ring-opening - the latter all evidently being stereospecific - to deliver enantioenriched cycloheptatrienes with embedded benzylic stereocentres.
对映体富集的七元碳环是许多具有结构和生物学意义的分子中的结构单元。我们报道了一种简单、实用、无过渡金属且机理独特的方法，用于对映选择性合成取代的环庚三烯。通过形成具有适当吸收带的有色烯醇盐并选择性地照射，我们启动了易于获得的α-苄基苯甲酰胺的串联、不对称阴离子和光化学扩环反应。导致产物的一系列反应包括用手性锂酰胺进行对映选择性苄基质子脱除、将所得构型确定的有机锂进行去芳构化环化以生成扩展的酰胺烯醇盐，以及光化学诱导的形式上的[1,7]-σ迁移重排和6π-电环化开环——后者显然都是立体专一性的——以提供具有嵌入苄基立体中心的对映体富集的环庚三烯。
