Patent ID: 8779160

Claim:
A process for preparing a compound corresponding to formula (I) wherein R 1 represents H or CH 3 , or a physiologically acceptable acid addition salt thereof, said process comprising: (a) reacting a compound corresponding to formula (a-1) with a compound corresponding to formula (a-2), in each case optionally in the form of an acid addition salt, in the presence of at least one mono- or diprotic acid promoting agent, wherein R 2 and R 3 in the compound of formula (a-2) together denote ═O, or together with the carbon atom connecting them form a cyclic moiety selected from the group consisting of wherein R 4 and R 5 each independently represent 0, 1, 2, 3 or 4 substituents selected from the group consisting of H and CH 3 , in a carboxylic acid reaction medium to form the compound of formula (I).