Microwave-Assisted Synthesis of Pyran-4-thione Derivatives

A solution of 3-hydroxy-2-methyl-4H-pyran-4-thione (thiomaltol; 200 mg, 1.41 mmol) in HCl (0.38 M, 2 mL) in a 10 mL microwave reaction vessel was treated with amine (3.1 mmol, 2.2 equiv). The heterogenous reaction mixture was sealed and stirred at 65 °C for 5 min prior to one microwave cycle of 1.5 min at 165 °C, 250 psi (max P), and 300 W. The reaction typically produced a yellow solution with a black, oily residue at the bottom of the tube. The reaction mixture was extracted with CH₂Cl₂ (2×) and the organic phase was dried (MgSO₄), vacuum filtered and evaporated in vacuo to give a dark residue. Purification by silica column chromatography (CH₂Cl₂ or 0–2 % MeOH in CH₂Cl₂) gave the desired product.