Preparation of S-2-halophenyl-2,1-benzothiazines.

Derivatives of 2,1-benzothiazines are useful synthetic intermediates for a variety of applications. We became interested in developing a one-pot procedure to S-2-halophenyl-2,1-benzothiazines as potential precursors to P,N type ligands for metals. Accordingly, we reacted S-2-halophenyl-S-methylsulfoximines with 2-bromobenzaldehydes using the Buchwald-Hartwig reaction under conditions previously developed in our laboratory. We found that 2-halophenylmethyl sulfoximines show lower reactivity in process than methylphenyl sulfoximine. Among the 2-(S)-2-halophenyl-(S)-methylsulfoximines tested, S-2-fluorophenyl-S-methyl sulfoximine was found to afford higher yields of benzothiazines than the bromine- or chlorine-substituted congeners. In the coupling of S-2-halophenyl-S-methylsulfoximines to 2-bromobenzaldehyde, using Ruphos as a ligand gave the best yields.