Efficient syntheses of 1,2,3,4,4a,5-hexahydro-pyrazino[2,1-c][1,4]benzothiazine-6,6-dioxide

Expeditious routes to 1,2,3,4,4a,5-hexahydro-pyrazino[2,1-c][1,4]benzothiazine-6,6-dioxide, a methylenesulfone-constrained arylpiperazine, have been developed. The key step forms the tricyclic system in a cascade of reactions via a 1,4-addition, nitrogen alkylation, and aromatic substitution sequence.