Transition metal-free, base mediated one-pot approach for the construction of the benzo[ b ][1,4,5]oxathiazepine 1-oxide core.

Herein, we have developed a base mediated, transition metal-free intermolecular epoxide ring opening by the nucleophilic attack of ortho -halogenated NH-sulfoximine followed by intramolecular aromatic nucleophilic substitution (S N Ar) for the synthesis of separable diastereomers of selected benzo[ b ][1,4,5]oxathiazepine 1-oxides. Both C-N and C-O bonds are formed simultaneously in a single step. This strategy has a good substrate scope and requires simple reaction conditions (room temperature) and cost-effective reagents, and shows good applicability for accessing sulfoximine analogues of benzoxathiazepine 1-oxide like bioactive skeletons. The absolute configurations of the separable major isomer 4z ( R , R ), minor isomer 4z' ( R , S ) and single isomer 4r ( R , R , S ) were confirmed by 2D NMR. On the other hand, the relative configuration of 4q ( S , R ) was assigned by 2D NMR along with X-ray crystal data analysis.