Diazo Coupling Route

The first reported calixarene diazo coupling involved the reaction of p-nitroben-zenediazonium tetrafluoroborate with Unexpectedly, it proceeded in an 

---

Azo Coupling. The coupling reaction between an aromatic diazo compound and a coupling component is the single most important synthetic route to azo dyes. Of the total dyes manufactured, about 60% are produced by this reaction. Other methods iaclude oxidative coupling, reaction of aryUiydraziae with quiaones, and oxidation of aromatic amines. These methods, however, have limited iadustrial appHcations. 

The reaction of azide ions with aliphatic diazo compounds was investigated by Kirmse et al. (1979 for a discussion see Zollinger, 1995, Sec. 6.1). Here we mention only that cyclopropanediazonium ions react similarly to the aromatic diazonium ions, i.e., by TV-coupling to 1-cyclopropylpentazene and dediazoniation to cyclopropyl azide. In about 60% of the 1-cyclopropylpentazene the cyclopropyl azide is formed directly by dediazoniation of the original diazonio group, while in 40% the route is via the cyclopropylpentazole. 

The synthetic route to monoazo yellow pigments involves the coupling of a diazo-tized substituted aniline with a coupling component containing an active methylene moiety in a linear structure. 

Figure 2.6 Schematic representation of routes to mono-, dis- and tris-azo dyestuffs. Symbols A is amine to be diazotised (also A ) E is end coupling component (i.e. terminal group) - (also E j D is a diamine than can be diazotised twice (tetrazotised) M is an amine that can be first coupled with A and then diazotised (also M ) Z is a coupling component that can couple twice with the same or different diazos ZXZ as for Z but with Xas a bridging group Dotted arrow is the -N=N- (azo) group.

Synthesis ofAzo Dyes. Processes to all the major benzene and naphthalene intermediates that are used in the commercial manufacture of azo dyes have been extensively reviewed. Description of the synthetic routes to heteroaromatic diazo components, such as those shown in Figure 2.8, are well covered in literature reviews, ° as are all the major heterocyclic coupling components. 

The aminophenyl glycosides can be coupled to activated supports by other routes. Thus, the glycosides may be converted into diazo-... 

The dipolar cycloaddition chemistry of isomunchnones is a powerful and concise route to polycyclic azaheterocycles, and Padwa has been the pioneer in this effort. Sheehan and Padwa employed the rhodium-catalyzed isomunchnone generation and subsequent trapping to a synthesis of 2-pyridones and the alkaloid ( )-ipalbidine (465) (Fig. 4.144). Thus ot-diazo imide 462 was readily constructed from 2-pyrrolidinone and allowed to react with rhodium acetate in the presence of c/i-l-(phenylsulfonyl)-l-propene to afford 2-pyridone 464 after loss of phenylsul-finic acid. Further manipulation, featuring a Stille coupling, gave ( )-ipalbidine 465. 

---