Rhodium-Catalyzed Regioselective Synthesis of Isocoumarins through Benzothiadiazine-Fused Frameworks
Prashant B Dalvi1, Kuang-Ling Lin1,2, Manohar V Kulkarni1
1Department of Applied Chemistry, National Chiao-Tung University , 1001 Ta-Hseuh Road, Hsinchu 300-10, Taiwan, ROC.
Abstract:
An unprecedented two-step, one-pot synthesis of benzimidazothiadiazine 5,5-dioxides is presented. Reaction condition based regioselectivity has been achieved where fused benzimidazo[1,2-b][1,2,4]thiadiazines are exclusively formed under thermal conditions, whereas benzimidazo[2,1-c][1,2,4]thiadiazines were created only under microwave irradiation. The salient features of this protocol include a regioselective sulfonylation of 2-aminobenzimidazole with o-halo sulfonyl chlorides followed by N-C bond formation. The acid forms of these fused regioisomers have been used to introduce novel guanidine-containing isocoumarin frameworks.
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