The utility of unconventional noncovalent interactions (NCIs) such as chalcogen bonding has lately emerged as a robust platform to access synthetically difficult glycosides stereoselectively. Herein, we disclose the versatility of a phosphonochalcogenide (PCH) catalyst to facilitate access into the challenging, but biologically interesting 7‐membered ring α,α’‐C‐disubstituted oxepane core through an α‐selective strain‐release C‐glycosylation. Methodically, this strategy represents a switch from more common but entropically less desired macrocyclizations to a thermodynamically favored ring‐expansion approach. In light of the general lack of stereoselective methods to access C‐septanosides, a remarkable palette of silyl‐based nucleophiles can be reliably employed in our method. This include a broad variety of useful synthons, such as easily available silyl‐allyl, silyl‐enol ether, silyl‐ketene acetal, vinylogous silyl‐ketene acetal, silyl‐alkyne and silylazide reagents. Mechanistic investigations suggest that a mechanistic shift towards an intramolecular aglycone transposition involving a pentacoordinate silicon intermediate is likely responsible in steering the stereoselectivity.

中文翻译：

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通过硫属键合催化应变释放 C-七烷基化策略立体选择性进入 α,α'-C-氧杂环庚烷支架

硫族键合等非常规非共价相互作用（NCI）的实用性最近已成为立体选择性地获取合成困难的糖苷的强大平台。在此，我们公开了膦硫族化物（PCH）催化剂的多功能性，可通过α-选择性应变释放C-糖基化促进进入具有挑战性但具有生物学意义的7元环α,α'-C-二取代氧杂环庚烷核心。从系统上来说，这种策略代表了从更常见但熵上不太理想的大环化到热力学上有利的扩环方法的转变。鉴于普遍缺乏获取 C-七糖苷的立体选择性方法，我们的方法可以可靠地使用一系列基于甲硅烷基的亲核试剂。这包括多种有用的合成子，例如容易获得的甲硅烷基-烯丙基、甲硅烷基-烯醇醚、甲硅烷基-乙烯酮缩醛、插烯甲硅烷基-乙烯酮乙缩醛、甲硅烷基-炔和甲硅烷基叠氮化物试剂。机理研究表明，涉及五配位硅中间体的分子内糖苷配基转位的机械转变可能是控制立体选择性的原因。