Indazolones compounds

Two double bonds. This is the most important class which includes the aromatic compounds pyrazole (3), indazole (4) and isoindazole (5), their non-aromatic isomers, pyrazolenines (or 3iL-pyrazoles 6), isopyrazoles (or 4JT-pyrazoles 7) and 3JT-indazoles (8), and the carbonyl derivatives of pyrazolines with the endocyclic double bond in positions 1, 2 or 3, i.e. (9), (10) and (11), respectively. The indazolones (12) and the pyrazolidinediones (13) and (14) also belong to this group. 

Azo compounds are reactive dienophiles. Indeed, one of the very first Diels-Alder reactions was the addition of diethyl azodicarboxylate to cyclopentadiene (equation 134)128 129. Other early examples of the reaction are the formation of tetrahydropyridazines from indazolone 252 and phthalazinedione 253 (equations 135 and 136)130. 

Dienophilic cyclic a-carbonylazo compounds (triazoline diones, indazolone, phthalazine dione) prepared in a flow cell, by anodic oxidation of the corresponding hydrazino compounds in acidic methanol or acetonitrile, react with dienes (Scheme 50) [72, 73]. 

From a qualitative viewpoint there is no doubt that the compounds classified as aromatic in Section 4.04.1.1 (pyrazoles, indazoles, isoindazoles, pyrazolones, indazolones, mesoionic derivatives) indeed have aromatic properties to a greater or lesser extent. Dihy-drobenz[cd]indazole (115) is also formally an aromatic compound since it has an odd number of electron pairs (n =7). However, due to the presence of two adjacent nitrogen atoms the aromatic tautomer (115a) is not stable, and the compound exists as the 1,5- or 1,3-dihydro tautomers (115b) or (115c) <72JCS(P2)68). The antiaromatic benz[cd]indazole (116), although unstable, has been fully characterized by N, H and NMR spectroscopy... 

Sodium tetrachloropalladate(II) 2-Aryl-3-indazolones from azo compounds via carbonylation... 

Phenylhydrazones of aromatic aldehydes also give phthalimidines [122, 691]. With the use of compounds labelled with it was shown that the nitrogen originally attached directly to the phenyl group of the phenyl-hydrazone is retained in the indazolone. 

Aromatic azo compounds react with carbon monoxide to form indazolones. At higher temperatures, further reaction of the indazolones leads to insertion of CO to form 2,4-dioxo-l,2,3,4-tetrahydroquinazolines [678,696]. 

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