Process for the preparation of tolterodine

A process for the preparation of tolterodine or a pharmaceutically acceptable salt thereof, comprising:

• A) reacting a compound of formula (II)
• in which when X is —CH2— then R is —(isopropyl)2;
• or when X is ═CO then R is —N (isopropyl)2 or —OR1, wherein R1 is an aryl or a straight or branched
• C1-C6 alkyl group, optionally substituted with phenyl;
• with an acidic agent;
• or
• B) reacting a compound of formula (III)
• wherein Y is a group able to provide a benzylic carbocation and Z is hydrogen or Y and Z, taken together, complete a double bond;
• and X and R are as defined above, with p-cresol and an acidic agent;
• to obtain, respectively, when in a compound of formula (II) or (III)
• a) X is —CH2— and R is —N(isopropyl)2, a compound of formula (I)
• i.e. tolterodine free base;
• or when
• b) X is ═CO and R is —N(isopropyl)2, a compound of formula (III)
• which by reduction yields tolterodine free base;
• or when
• c) X is ═CO and R is a —OR1 group wherein R1 is as defined above, a compound of formula (IV)
• wherein R1 is as defined above, which is converted to tolterodine free base;
• and, if desired, the conversion of tolterodine free base to a pharmaceutically acceptable salt thereof.