Sequential Ester Homologation–Nucleophile‐Guided Functionalization: A Chemoselective Access to Thioesters, Amides, and Acids

The homologation of esters—in the presence of a lithium carbenoid—to thioesters, amides, and carboxylic acid is reported. By controlling the tetrahedral intermediate collapsing and promoting a series of rearrangements ultimately leading to a high electrophilic ketene, the subsequent incorporation of S-, N-, and O-nucleophilic elements furnishes the title compounds. Despite the coexistence of multiple (concomitant) equilibria and short-living entities, the protocol features remarkable chemocontrol and flexibility. Notably, the formal oxidation state of the final compounds is retained.