合成路线1

Condensation between 1,2-difluoro-4-nitrobenzene (I) and L-prolinol (II) affords the N-aryl prolinol (III). Subsequent conversion of alcohol (III) into bromide (IV) is achieved by treatment with CBr4 and PPh3. Displacement of bromide (IV) with sodium thioacetate, followed by basic hydrolysis of the resultant thioacetate ester (V) leads to thiol (VI). Intramolecular cyclization of (VI) in the presence of NaH generates the pyrrolobenzothiazine system (VII). Catalytic hydrogenation of the nitro group of (VII) gives amine (VIII), which is acylated by benzyl chloroformate to provide carbamate (IX). The lithium anion of carbamate (IX) is condensed with (R)-glycidyl butyrate (X) to furnish oxazolidinone (XI). Then, treatment of alcohol (XI) with methanesulfonyl chloride produces mesylate (XII).