Pyrazolo- -benzothiazines

The pyrazolo[5,l-c] 1,2,4-triazoles 56 have recently been prepared (86JHC43) from 8-thioxo-l,3-benzothiazines (52) and thiocarbohydrazide (51) through the mesoionic intermediates (53) and triazolothiadiazines (54). 

The reaction of 3-benzoyl- (or 3-acetyl) -4-hydroxy-2//-1,2-benzothiazine 1,1-dioxide (89) with hydrazine to produce pyrazolo[4,3-c][l,2]benzothia-zine 5,5-dioxide derivatives was discussed in Section II,B,1 (See Eq. 22). Steiner141 recently reacted 3-acetyl-1,2-benzothiazines (196) with alkyl-substituted hydrazines the hydrazones (197) were usually not isolated but cyclized directly to l-substituted-l,4-dihydro-3-methylpyrazolo[4,3-c][l,2]-benzothiazine 5,5-dioxides (198) (Eq. 44). 

Likewise, the 3-allenyl-derivatives (48) yield the corresponding pyrazolo[3,2-c][l,4]-benzothiazines... 

R = Ph, = C02Et) formation of the pyrazolo-l,4-benzothiazine (49) is accompanied by the novel diazeto[2,3-c][l,4]benzothiazine (50 13%), for which an x-ray crystal structure has been obtained <84AX(C)I476>. 

---