Cyclyzation of lapachol induced by thallium salts

摘要

This work describes the cyclization of lapachol (1) induced by thallium triacetate (TTA) and thallium trinitrate (TTN) in several solvents using magnetic stirring and under microwave irradiation. a-Xyloidone (2) - dehydro-a-lapachone - was obtained as the main product in these reactions in 20 75% yield. However, rhinacanthin-A (4) was isolated as main product in a 40% yield, using TTA and acetic anhydride:water (1:1) as solvent, and dehydro-iso-a-lapachone (3) in 21% yield, using TTA and dichloromethane as solvent. The reaction time decreased drastically under microwave conditions, but the yields of these reactions were not the expected.