Multicomponent Reactions of 1,3-Cyclohexanediones and Formaldehyde in Glycerol: Stabilization of Paraformaldehyde in Glycerol Resulted from using Dimedone as Substrate

Glycerol has proved to be an effective promoting medium for many multicomponent reactions of 1,3-cyclohexanediones and formaldehyde. Styrenes, airlines. 2-naphthol, 4-hydroxy-6-methyl-2-pyrone and 4-hydroxy-1-methyl-2-quinolone could easily react with 1,3-cyclohexanediones and paraformaldehyde in glycerol under catalyst-free conditions to afford a variety of complex skeletons in fair to excellent yields. In these reactions, glycerol not only showed a significant promoting effect on the reaction yields but also endowed the reaction system with many typical properties of green chemistry, such as cheap., renewable, recyclable and biodegradable solvent, good safety and easy separation of product. The promoting effect of glycerol for the three-component reaction of styrene, dimedone and paraformaldehyde could be attributed to a restricted formation of the methylene intermediate in glycerol. During the reaction, a physical Shell, which is mainly composed of a by-product generated in the beginning of the reaction, might be formed in the Surface of paraformaldehyde and plays a key role in controling the formation of the intermediate by means of restricting the decomposition of paraformaldehyde.