Masked formylation of activated aromatics via dithianes and a mild, sustainable cleavage protocol

Abstract

Here we describe a masked formylation strategy based on the activation of 1,3-dithiane oxide with oxalyl chloride. The reaction proceeds through a thionium ion intermediate, enabling efficient electrophilic aromatic substitution with electron-rich arenes and heteroarenes. The method shows good tolerance toward alkyl-, hydroxyl-, and alkoxy-substituted phenols, as well as indoles, while thiophenols react preferentially at sulfur, supporting a Pummerer-type pathway. In addition, we developed a practical oxalyl chloride-mediated dithiane cleavage protocol, affording aldehydes in good to excellent yields. Dithiolanes were also reactive but generally less efficient. Overall, this work introduces oxalyl chloride as a versatile reagent for masked formylation and dithiane cleavage, providing operationally simple and broadly applicable synthetic methodologies.