Microwave assisted synthesis of some new 2-substituted-1,4-benzothiazine derivatives

Department of Chemistry, Shivaji University, Kolhapur-416 004, Maharashtra, India

E-mail : m_ deshmukh1@rediffmail.com

Manuscript received 17 June 2008, revised 12 April 2010, accepted 12 April 2010

The nitrogen and sulphur containing compounds are well known for their vital role in medicinal chemistry. Here, we report the synthesis of 2-hydrazido-1,4-benzothiazine (2) from 2-carbethoxy 1,4-benzothiazine-3-(1H)-one (1) and hydrazine hydrate which then treated with acetyl acetone, ethyl acetoacetate, cyanoethylacetate to give substituted 2-(benzothiazine-3-one-2-yl-oxo)-3,5-dimethyl pyrazole (2a), 1-(benzothiazine-3-one-2-yl-oxo)-3-methyl pyrazole-5-one (2b) and (1-benzothiazine-3-one-2-yl-oxo)-3-amino pyrazole-5-one (2c) respectively under microwave irradiation. Further, the reaction or 2 with phenyl isothiocyanate under microwave irradiation yielded 1-(benzothiazolyl-oxo)-4-phenyl thiosemicarbazide (2d) which was subsequently cyclised with cone. H₂SO₄ and dil. NaOH to give targeted 2-(benzothiazin-3-one-2-yl)-5-anilino-1, 3,4-oxadiazole (2e) and 1-phenyl-2-[benzothiazine-3(1H)-one-2-yl]-5-mercapto-1 ,3,5-triazole (2f) respectively.