We report herein the tetraethylammonium bromide catalyzed intramolecular oxidative cyclization of O- or S-alkylated salicylic or thiosalicylic acid derivatives to access 4H-benzo[d][1,3]dioxin-4-ones or 4H-benzo[d][1,3]oxathiin-4-ones, respectively. The oxidative cyclization of salicylic acid derivatives proceeds through a radical pathway at 110 °C. In contrast, the cyclization of the thiosalicylic acids proceeds smoothly at room temperature via an ionic pathway. Notably, the overall reactions are fast, completed within short reaction times, furnishing the products in high yields and with smooth formation of quaternary carbon centers.
Key words
metal free reactions - cyclization - Csp
3–H activation - ethers - thioethers
