Nitrosation of 7-chloro-3,4-dihydro-2H-1,4-benzothiazine (I) by means of NaNO2 and H2SO4, followed by reduction with LiAlH4, affords amino derivative (II). Finally, Fischer indole cyclization of (II) with 4-chlorobutanal (III) in refluxing aqueous methanol yields the desired product.