Pyrazolo pyrazoles, bromination

Pyrazolo[l,2-a]pyrazoles give 3-bromo products unless the 3-position is blocked by a methyl when bromomethyl products arise (80JA4983 81JOC1666, 87JOCI673). When all of the pyrazole ring positions are filled by phenyl groups, chlorination and bromination occur in thepara-positions (74BCJ946) (see also B, 1,2). 

Bromination of pyrazolo[2,3-c][l,2,4]triazines (179) occurred only in the pyrazole ring (83AP697). 

The reaction of differently substituted 5-arylidenehydrazono-4-ethoxycarbonyl-3-methyl-(l/7)pyrazoles 194 (X = 2-NC>2, 4-NC>2, 2-Cl, 4-Me, 4-NMe2, 2-OMe) with bromine in acetic acid in the presence of sodium acetate leads mainly to 3-aryl-7-ethoxycarbonyl-6-methyl-(li/)pyrazolo[5,l-c][l,2,4]triazoles 195 (Scheme 7) <1977J(P1)2047>. 

Aldehydes, arylideneanilines, carboxylic acids and orthoesters have been used as one-oarbon units for binding the two amino functions of 4-amino-l-alkyl-3-propylpyrazole-5-oarboxamide to give l,6-dihydro-pyrazolo[4,3-<7]pyrimidin-7-ones <05MC619 05JHC751>. A modified efficient synthesis of variably substituted pyrazolo[4,3-<7]pyrimidm-7-ones has been described using a pyrazole-5-carboxylic acid, which was selectively brominated at position 4 and then converted into the carboxamide. Microwave irradiation gave better yields in the conversion of the carboxamides to pyrazolo[4,3-J]pyrimidinones <05JHC1085>. 

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