Synthesis of thiopyran derivatives [4 + 2] cycloaddition reactions.

In this review, we provide a comprehensive overview of the synthesis of thiopyran family compounds cycloaddition reactions, with examples spanning from the year 2000 to the present. We have categorized the [4 + 2] cycloaddition processes using several criteria, particularly distinguishing between intermolecular and intramolecular types based on the Diels-Alder partners. Additionally, from a mechanism standpoint, we differentiate between concerted and stepwise [4 + 2] processes, offering an analysis of these mechanisms based on the current literature.