Pyrazolone-azomethines

Hydrazono-5-(p-dialkylaminophenylimino)seienazoles, pyrazolone azomethin selenazoles, quinoid dyes, and formazans are other important dyes used in photography and the color industry (cf. previous sections). 

By further reaction of the selenazole-pyrazolones with p-nitro-sodialkylanilines a number of pyrazolone-azomethines (18) was pre-... 

Pyrazolone azomethin selenazoles, dyes, photography and color industry,... 

A new class of free radical photoinitiators such as 499 (Figure 33) <1998CM3555> have been developed based on pyrazolone azomethine dyes. 

Despite the inconveniences, a certain number of studies have been carried out, particularly concerning dyes containing azomethine groups. Such as hydrazones, pyrazolones, formazans, and selenazoles quinoids. Saturated heterocycles, that is, selenazolines and selenazolidines. have also been tackled. Selenium derivatives for pharmacological or physiological applications are little developed by comparison with their thiazole homologs. 

Thus, o,o -dihydroxyazo (8), o.o -hydroxyaminoazo (9), o,o -carboxyhydroxy-azo (10), o,o -dihydroxyazomethine (11), and o,o -carboxyhydroxy azomethine (12) residues yield with metals stable annelated 5,6- and 6,6-membered ring systems, respectively (Scheme 2.13). The residues in the azo compounds are in most cases benzene, naphthalene, pyrazolone or open-chain enol-keto systems, while in the azomethine compounds they are mostly benzene systems. 

Copper-catalyzed 1,3-dipolar cycloaddition of azomethine imine 264 with ethyl propiolate 265 with a chiral ferrocenyl bidentate ligand efficiently generated dihydropyrazol[l,2- 7]pyrazolones 266 in very good yields and ee... 

Kobayashi and co-workers successfully achieved the asymmetric 1,3-dipolar cycloaddition reaction of azomethine imines with terminal alkynes catalyzed by CuHMDS and DIP-BINAP ligand to provide N,N-bicyclic pyrazolidinone derivatives in high yields with exclusive regioselectivity and excellent enantioselectivity (Scheme 26) [46]. Mechanistic studies elucidated a stepwise reaction pathway and revealed that the steric character of the ligand determines the regioselectivity. Arai and co-workers applied chiral bis(imidazolidine)pyridine-CuOAc complex to the [3+2]cycloaddition of azomethine imines with propiolates for the construction of bicyclic pyrazolo[l,2-a]pyrazolone derivatives with up to 74% ee [47]. 

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