Synthesis and Reactivity of 2-Polyfluoroalkyl Thiopyrylium Salts

Significance

The synthesis and reactivity of 2-polyfluoroalkyl thiopyrylium salts is reported. The construction of the thiopyrylium ring system begins with the hetero-Diels-Alder reaction between polyfluorothioalkanoyl chloride and buta-1,3-diene to generate the 2H-thiopyran, which is aromatized to give the thiopyrylium perchlorate or tetrafluoroborate salt. Its reaction with a range of oxygen-, nitrogen-, sulfur-, and carbon-centered nucleophiles gave the 2- and 4-substituted thio­pyrans in moderate to good yields. In general, ­oxygen-centered nucleophiles gave exclusively the 2-substituted isomer, whereas softer nucleophiles, such as diazomethane, gave increasing quantities of the 4-substituted product (ratio of 1/2 = 33:66). In addition, the reactivity of the conjugated system in 1 to dihydroxylation was examined briefly.