Synthesis of 6-substituted-2,3-dihydro-1H-imidazo[1,5-b]pyrazoles

Fused Imidazopyrazoles: Synthetic Strategies and Medicinal Applications

“…2,3-Dihydroimidazo [1,5-b]pyrazoles 84 containing a structurally heterocyclic system corresponding to cyclized histamine were prepared by cyclodehydration of substituted N-(3-pyrazolylmethyl)acetamides 80 or N-(3-pyrazolylmethyl)acetamides 83, obtained by the catalytic hydrogenation of 1-benzoyl-4,5dihydro-1H-pyrazole-3-carbonitriles 79 followed by acylation. These latter precursors 79 were conveniently obtained by the cycloaddition of substituted acrylonitriles with CH 2 N 2 followed by in situ benzoylation using benzoyl chloride [48] (Scheme 20). [1,5-b]Pyrazole.…”

Synthesis and Crystal Structures of 4,5-Dihydroimidazo[1,5-b]pyrazol-6-ones

“…32,33,36,40,41 However, synthetic methodology for obtaining imidazo [1,5-b]pyrazole derivatives is notably lacking, and very little is known about these compounds. 3,4 Only a few individual examples having this uncommon ring fusion have been previously prepared; for example, by cyclodehydration of substituted pyrazolylmethylacetamides leading to 2,3-dihydroimidazo [1,5-b] derivatives related to cyclized histamine, 43 preparation of 2,3-dihydro-1H-imidazo [1,5-b]pyrazole-4,6(3aH,5H)-dione from 1-(benzylideneamino)-5-(2-hydroxyethyl)hydantoin, 44 and the synthesis of hexahydro-4,4-dimethyl-1,3a-diaryl-6-oxo-1H-imidazo [1,5-b]pyrazole-3-carbonitriles from -aminoisobutyrophenone phenyl hydrazones. 45 Concerning imidazopyrazolones, studies on the synthesis, properties and usefulness of substances exhibiting [1,2-b], [46][47][48][49][50] [4,5-c], 51,52 and [3,4-b] 45 ring systems have been successful.…”