Fragmentation of glucosylphosphonium ylides for the synthesis of glycals†

Abstract

Metal-free carbenes are high-energy reactive intermediates that have been harnessed for numerous useful transformations. However, access to these versatile intermediates is often limited by the requirement for highly energetic diazoalkane precursors, which release thermodynamically stable N₂ as an enthalpic driving force. Herein, we report the formal homolysis of a common phosphonium ylide to generate a useful carbene intermediate. This strategy enables the direct transformation of glucosylphosphonium ylides into glycals, involving the formation of a glycosylidene carbene intermediate and a subsequent 1,2-H migration. Furthermore, theoretical calculations rationalize the chemical driving force behind the homolytic fission of phosphonium ylide bonds and propose an acid–base pair model of phosphonium ylides, namely phosphine-protected carbenes. This study presents a novel method for preparing metal-free carbenes and expands the applications of phosphonium ylides.