Process for preparing analgesic carboxylic acid amide derivatives

Analgesic compounds are of the general formula (I): in which, R and R each represents hydrogen or C1-C6 alkyl, or R and R together with the nitrogen atom to which they are attached form a heterocycle; E represents methylene, sulphur, oxygen or imino group optionally substituted with C1-C6 alkyl or aralkyl; ring A is aryl or heteroaryl ring, optionally substituted; R is hydrogen or C1-C6 alkyl and R is hydrogen or R and R together represent a group of formula (IV): -(CRR)m-C(=Y)- (IV) (wherein R and R is C1-C6 alkyl or hydrogen, up to a maximum of 3 alkyl groups, m is 1, 2, or 3, and Y is two hydrogens or oxygen); provided that when E represents a methylene group, then R is a C1-C6 alkyl group or R and R together represent a group of the formula (IV).