N-Benzoyl-N-methylsulfonyl anthranilates: unexpected cyclization reaction to 4-alkoxy-2,1-benzothiazines

The synthesis of 4-alkoxy-1H-2,1-benzothiazine 2,2-dioxide derivatives was achieved through an unexpected base-mediated cyclization of N-benzoyl-N-methylsulfonylanthranilates. A reaction mechanism involving the sulfene species has been postulated. The obtained 4-alkoxy derivatives can be further functionalized at the N-1 position allowing unsymmetrically N,Odisubstituted 1H-2,1-benzothiazines 2,2-dioxide to be prepared.