1. A method of preventing the development of or treating dyskinesias in a patient being treated for Parkinson's disease comprising the step of administering to said patient a pharmacologically effective amount of a compound of formula (I), or a pharmaceutically acceptable salt thereof, 2 1 and R 2 are independently H, provided that both are not H, —OH, CN, CH 2 CN, 2- or 4-CF 3, CH 2 CF 3, CH 2 CHF 2, CH&boxH;CF 2, (CH 2 ) 2 CF 3, ethenyl, 2-propenyl, OSO 2 CH 3, OSO 2 CF 3, SSO 2 CF 3, COR, COOR, CON(R) 2, SO x CH 3, SO x CF 3, O(CH 2 ) x CF 3, where x is 0-2, SO 2 N(R) 2, CH&boxH;NOR, COCOOR, COCOON(R) 2, C 1-8 alkyls, C 3-8 cycloalkyls, CH 2 OR, CH 2 (R) 2, NRSO 2 CF 3, NO 2, halogen, phenyl in positions 2, 3 or 4, thienyl, furyl, pyrrole, oxazole, thiazole, N-pyrroline, triazole, tetrazole or pyridine; R 3 is hydrogen, CF 3, CH 2 CF 3, C 1-8 alkyl, C 3-8 cycloalkyl, C 4-9 cycloalkyl-methyl, C 2-8 alkenyl, C 2-8 alkynyl, 3,3,3-trifluoropropyl, 4,4,4-trifluorobutyl, —(CH 2 ) m -R 5, where m is 1-8, CH 2 SCH 3 or a C 4-8 alkylene bonded to the N-atom and one of its adjacent carbon atoms to form a heterocyclic structure; R 4 and R are independently selected from hydrogen, CF 3, CH 2 CF 3, C 1 -C 8 alkyl, C 3-8 cycloalkyl, C 4-9 cycloalkyl-methyl, C 2-8 alkenyl, C 2-8 alkynyl, 3,3,3-trifluoropropyl, 4,4,4-trifluorobutyl, or —(CH 2 ) m -R 5, where m is 1-8; R 5 is phenyl, phenyl substituted with CN, CF 3, CH 2 CF 3, C 1-8 alkyl, C 3-8 cycloalkyl, C 4-9 cycloalkyl-methyl, C 2-8 alkenyl or C 2-8 alkynyl, 2-thiophenyl, 3-thiophenyl, —NR 6 CONR 6 R 7 or CONR 6 R 7 ; and R 6 and R 7 are independently hydrogen, C 1-8 alkyl, C 3-8 cycloalkyl, C 4-9 cycloalkyl-methyl, C 2-8 alkenyl or C 2-8 alkynyl.