A Silicon/Sulfur Analog of an Acyl Anion With Ambident Reactivity

ABSTRACT Acyl anion‐based umpolung is a foundational strategy in synthetic chemistry that enables reversal of the intrinsic electrophilic polarity of carbonyl compounds. Although acyl anion chemistry has been well developed, translating this polarity‐inversion concept to heavier main‐group congeners has remained elusive. Here we report the synthesis of a silicon/sulfur analogu of an acyl anion through a distinctive four‐electron reductive rearrangement of an arylthiotribromosilane precursor. Structural and computational analyses reveal a polarized Si═S interaction and lone pair at the silicon center, endowing it with acyl‐anion‐type electronic character. The resulting anion exhibits ambident nucleophilic reactivity of the silicon and sulfur centers. Reactions with Fe 2 (CO) 9 and organic azides demonstrate chemically accessible lone‐pair reactivity at silicon, whereas sulfur‐centered functionalization with chlorophosphine and chlorosilane electrophiles affords neutral acyclic silylenes. These findings establish a strategy for translating classical carbonyl umpolung concepts into low‐valent silicon chemistry and provide access to electronically cooperative main‐group frameworks featuring dual reactive sites.