Solvent-free conjugated addition of thiols to citral using KF/alumina: preparation of 3-thioorganylcitronellals, potential antimicrobial agents

A general, clean and easy method for the conjugated addition of thiols to citral promoted by KF/Al2O3 under solvent-free conditions at room temperature or under MW irradiation is described. It was found that the same protocol is applicable to the direct reaction of thiophenol with essential oil of lemon grass (Cymbopogon citratus) to afford directly 3-thiophenylcitronellal, a potential bactericide agent. The method was extended to others electron-poor alkenes with excellent results. The catalytic system can be reused up to three times without previous treatment with comparable activity.