NOVELTY - Preparation of lurasidone hydrochloride (I) comprises (a) reacting ((1R,2R)-2-(methylsulfonyloxymethyl)cyclohexyl)methyl methanesulfonate (IV) and 3-piperazin-1-yl-benzo(d)isothiazole (V) to yield 3-((3aR,7aR)-spiro(1,3,3a,4,5,6,7,7a-octahydroisoindol-2-ium-2,4'-1,4-diazinan-4-ium)-1'-yl)-1,2-benzothiazole mesylate (III); (b) reacting (III) with 4-aza-tricyclo(5.2.1.0)decane-3,5-dione (II) in the presence of an organic base to yield lurasidone base; (c) converting lurasidone base to an acid addition salt of lurasidone; and (d) converting the acid addition salt to lurasidone hydrochloride.    USE - (I) is useful as a psychotropic substance in the treatment of schizophrenia and bipolar disorders. No biological data given.    ADVANTAGE - The process is simple, economical, efficient, robust and environmentally friendly and provides high yields and purity of lurasidone hydrochloride. The process uses less toxic reagents, and can be applied on an industrial scale without the formation of impurities which are hard to remove. The process is more practical from an industrial point of view to proceed with the one-pot reaction.    DETAILED DESCRIPTION - Preparation of lurasidone hydrochloride of formula (I) comprises (a) reacting ((1R,2R)-2-(methylsulfonyloxymethyl)cyclohexyl)methyl methanesulfonate of formula (IV) and 3-piperazin-1-yl-benzo(d)isothiazole of formula (V) in a solvent having a boiling point greater than 80 degrees C in the presence of an organic base having a base dissociation constant (pKB) greater than 10, to yield 3-((3aR,7aR)-spiro(1,3,3a,4,5,6,7,7a-octahydroisoindol-2-ium-2,4'-1,4-diazinan-4-ium)-1'-yl)-1,2-benzothiazole mesylate of formula (III); (b) reacting (III) with (1R,2S,6R,7S)-4-aza-tricyclo(5.2.1.0)decane-3,5-dione of formula (II) in a solvent having a boiling point greater than 80 degrees C in the presence of an organic base having a pKB greater than 10, to yield lurasidone base; (c) converting lurasidone base to an acid addition salt of lurasidone with an organic carboxylic acid having an acid dissociation constant (pKA) lower than 3; and (d) converting the acid addition salt of lurasidone to lurasidone hydrochloride.