NEW MATERIAL:The compound of formula I (R1 is alkyl; R2 is H or alkyl). EXAMPLE:The compount of formula II. USE:Useful as a raw material of a novel unsaturated carboxylic acid ester which is useful as a medical and dental material. PROCESS:The compound of formula I can be prepared by (1) reacting the hydroxycarboxylic acid of formula III with trimethylolalkane of formula IV in a proper solvent (e.g. benzene, toluene, etc.) in the presence of an acid catalyst (e.g. p- toluenesulfonic acid, sulfuric acid, etc.) preferably in an inert gas atmosphere, and (2) dehydrating the resultant compound of formula V under heating preferably at 140-220 deg.C under reduced pressure of preferably about 1-0.03mm.Hg, in the presence of p-toluenesulfonic acid, sulfuric acid, etc.
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