TETRAHYDROPYRIDO (1,2-A) INDOLE DERIVATIVES, PROCESS AND INTERMEDIATES FOR THEIR PREPARATION AND PHARMACEUTICAL COMPOSITIONS CONTAINING THEM

A compound of the formula (I) or a pharmaceutically acceptable salt thereof: (I) wherein: R1 is hydrogen, C1-6 alkyl, C1-6 alkoxy or halogen; R2 and R3 are both hydrogen or together represent a bond; R4 is hydrogen and R5 is hydrogen or R4 and R5 together represent an oxo group; R6 is C1-7 alkyl substituted by NR8R9 where R8 and R9 are independently hydrogen or C1-4 alkyl or together are C3-7 polymethylene optionally containing a further hetereoatom which is oxygen, sulphur or nitrogen substituted by R10 where R10 is hydrogen, C1-4 alkyl or benzyl, and optionally substituted by one or two C1-4 alkyl, C2-5 alkanoyl, C1-4 alkoxycarbonyl, aminocarbonyl optionally substituted by one or two C1-6 alkyl groups or by a benzyl group, cyano, phenyl or benzyl and wherein any phenyl or benzyl group is optionally substituted in the phenyl ring by one or two halo, CF3, C1-4 alkyl, C1-4 alkoxy, cyano or nitro groups; and R7 is hydrogen or C1-4 alkyl.