Process for the preparation of indolone derivative

A process for the preparation of 4-[2-(Di-n-propylamino)ethyl]-2,3-dihydro-1H-indol-2-one of formula (I) and its pharmaceutically acceptable salts, solvates Formula I involving new intermediates of compound of formula (A) and (B) wherein R represents (i) a halogen atom selected from fluorine, chlorine atom, bromine atom and iodine atom; (ii) lower alkanesulfonyloxy group selected from methanesulfonyloxy, ethanesulfonyloxy, isopropanesulfonyloxy, propanesulfonyloxy, butanesulfonyloxy, tert-butanesulfonyloxy, pentanesulfonyloxy, hexanesulfonyloxy; (iii) substituted or unsubstantiated arylsulfonyloxy group selected from phenylsulfonyloxy, 4-methylphenylsulfonyloxy, 2-methylphenylsulfonyloxy, 4-nitrophenylsulfonyloxy, 4-methoxyphenylsulfonyloxy, 3-chlorophenylsulfonyloxy; (iv) arylalkylsulfonyloxy group selected from benzylsulfonyloxy, 2-phenylethylsulfonyloxy, 4-phenylbutylsulfonyloxy, 4-methylbenzylsulfonyloxy, 2-methylbenzylsulfonyloxy, 4-nitrobenzylsulfonyloxy, 4-methoxybenzylsulfonyloxy, 3-chlorobenzylsulfonyloxy.