Synthesis of novel 1,2,5-benzothiadiazepine 1,1-dioxides

3-Methoxycarbonyl-2-N-methyl-1,2,5-benzothiadiazepine 1,1-dioxide 2b can be obtained in seven unambiguous steps starting from commercially available l-serine methyl ester. The crucial step in the synthesis of 2b is the intramolecular Michael addition of dehydroalanine derivative 17, which can be achieved using sodium tert-butoxide as a non-nucleophilic base. An initial attempt to construct the same scaffold via an alternative strategy, which was based on a nucleophilic aromatic substitution as the key ring-closing step, proofed to be unsuccessful.