Process for preparing 5,6-dihydro-4-(S)-(ethylamino)-6-(S) methyl-4H-thieno[2,3b]thiopyran-2-sulphonamide-7,7-dioxide HCI

A process for preparing 5,6-dihydro-4-(S)-(ethylamino)-6-(S)methyl-4H-thieno[2,3b]thiopyran-2-sulphonamide-7,7-dioxide hydrochloride of formula (I),

• the process comprising
• (a) reacting compound of formula II wherein X is halo, with magnesium metal and treating the generated Grignard reagent in a solvent in situ with sulfur, triethyl amine hydrochloride, crotonic acid and suitable base to obtain compound of formula III,
• (b) reacting compound of formula III with a chlorinating agent to obtain a acid chloride, followed by subjecting the acid chloride to cyclisation in the presence of a Lewis acid to obtain a compound of formula IV;
• (c) reacting compound of formula IV with a mixture of chlorosulphonic acid and a chlorinating agent to form a sulphonylchloride of formula XX, extracting the sulphonylchloride in a chlorinated solvent, washing with water, drying and evaporating the chlorinated solvent to obtain compound of formula V;
• (d) reducing compound of formula V to obtain compound of formula VI;
• (e) oxidising compound of formula VI to obtain compound of formula VII;
• (f) subjecting compound of formula VII to a Ritter reaction to obtain compound of formula VIII
• (g) reducing compound of formula VIII to obtain compound of formula IX
• (h) converting compound of formula IX to acid addition salt thereof of formula XXI and recrystallizing enriched salt from the solvent and then converting salt of formula XXI to compound of formula X
• (i) resolving compound of formula X into compound of formula I.