Pyridinones, conversion into

Early synthetic work on the conversion of kojic acid into 3-hydroxy-4-pyridinones was instigated in the hope of finding potential anesthetics (25), but the results of this search proved disappointing. However, various investigators over the subsequent seven and a half decades have found a range of specialized applications and potential uses for several hydroxypyridinones, a few of which are mentioned later. 

The 1 phenacyl-2( 1 //)-pyridinone (66) is cyclized to the oxazolo[3,2-a]pyridinium salt (67) by sulfuric acid (67JHC66). Sometimes the loss of a proton can give a neutral product as in the conversion of (68) into the ring-fused system (69) (71JOC222). For further examples see Section 3.3.3.4.1 CHEC 4.29 CHEC-II, 8.10.3 and 8.10.5. F... 

Numerous structures containing the thiocarbonyl ylide dipole are conceivable. Incorporation of the thiocarbonyl ylide dipole into a bicyclic heterocyclic system is possible by the conversion of the cyclic thione (203) into the ring-fused mesoionic system (204). The thiocarbonyl ylide dipole (205) undergoes cycloaddition with both alkenic and alkynic electron-poor dipolarophiles in refluxing benzene or xylene so that, after extrusion of hydrogen sulfide or sulfur, respectively, from the initial 1 1 cycloadducts (206) and (207), a ring-fused pyridinone is formed. The method has been used for the annelation of pyridinones to the imidazole, 1,2,4-triazole, thiazole and 1,3,4-thiadiazole systems... 

---