Zinc-acetic acid reduction of 6-chloro-2,3-dihydro-1,3-dioxo-2-(2-pyridinylmethyl)-1H-isoindole-5-sulfonamide. Zinc dust (0.5 mole) is added in one portion to the 1,3-dioxoisoindole (0.1 mole) of part (a) in 800 ml. of acetic acid. The reaction mixture is stirred at room temperature for 1.0 hr. and then heated to reflux for a 6 hr. period during which time additional 9.0 g. portions of zinc are added at the end of 3, 4, and 5 hr., respectively. After stirring overnight, the reaction mixture is filtered and the filtrate concentrated to dryness under reduced pressure with additional water added to the residue and removed in vacuo to remove traces of acetic acid. Residual material is slurried in water, filtered, and the filtrate concentrated to dryness. Residual material is stirred with saturated sodium bicarbonate solution and an immiscible organic solvent such as hot ethyl acetate. The organic fraction is separated, dried over MgSO4 and concentrated to provide the product as the free base. The free base taken up in dimethylformamide and acidified with ethanolic hydrogen chloride affords 6-chloro-2,3-dihydro-3-oxo-2-(2-pyridinylmethyl)-1H-isoindole-5-sulfonamide hydrochloride.
