ORGANOPHOSPHORUS CHEMISTRY, 20.1 THE BEHAVIOUR OF CERTAIN γ-PYRONE DERIVATIVES TOWARD 2,4-BIS-(4-METHOXYPHENYL)-1,3,2,4-DITHIAPHOSPHETAN-2,4-DISULPHIDE (LAWESSON REAGENT)

Abstract Lawesson reagent LR,1 converts 2.6-dimethyl-y-pyrone 2a. flavone 3a into their corresponding thioketones 2b and 3b in high yields. Thiation of flavone 3a with Lawesson reagent LR,1 can be also induced photochemically to give thioflavone 3b together with the ring phosphorane product 6A. Thiation of khellin 4a by LR to give 4b is accompanied by demethylation of 4b to give desmethylthiokhellin 4c. The behaviour of γ-pyrones 2a, 3a and 4a toward thiation with LR,1 was discussed in the light of the principle of vinylogy.