Diazo-pyridine compound

In a flash photolysis study of a series of diazo carbonyl compounds, a correlation was found between the amount of carbene that could be trapped by pyridine and the amount of s-trans ketone.240... 

From Diazo Compounds via 1,3-Dipolar Cycloaddition. This method has been utilized widely in heterocychc chemistry. Pyrazohne (57) has been synthesized by reaction of ethyl diazoacetate (58) with a,P-unsaturated ester in the presence of pyridine (eq. 12) (42). 

In the context of their new synthetic route to arenediazo phenyl ethers (see Sec. 6.2), Tezuka et al. (1987 a, 1989) investigated the reaction products of phenyldi-azo 1-naphthyl ether (12.10) under various conditions. When an acetonitrile solution of the diazo ether 12.10 was kept standing at room temperature for one week in the dark, the 4- and 2-phenylazo-l-naphthol isomers (12.11 and 12.12) were formed in 48% (20%) and 9% (8%) yields respectively. In the presence of acid (aqueous HC1 or H2S04) or of various bases (aqueous NaOH, pyridine, aniline, or sodium acetate) the yields of the azo products are much lower, but higher proportions of biphenyl, 1-naphthol, and phenol are formed. The crosscoupling product l-phenylazo-2-naphthol was not detected when the reaction was carried out in the presence of 2-naphthol. As this mechanistic test reaction gave rather low yields of the two azo compounds 12.11 and 12.12 in the presence and absence of 2-naphthol,... 

All this is not to say that dialkylcarbenes are incapable of the reactions formerly attributed to them exclusively. They often—usually—are able to do the reactions, even in cases in which diazo compound chemistry pre-empts their doing so. For example, homocubylidenes (65) are not the first-formed intermediates from the diazohomocubane precursor (66). The bridgehead alkenes, homocubenes (67) are. However, it was possible to use a complex kinetic analysis involving both the pyridine ylide technique and the alternative hydrocarbon precursor 68 to show that in the parent system the two reactive intermediates 65 and 67 are in... 

HF-pyridine reagent, however, can also be used for the hy-drofluorination of alkenes,7 alkynes,7 cyclopropanes,7 and diazo compounds,8 the halofluonnation of alkenes,9 the preparation of fluoroformates from carbamates,10 the preparation of a-fluorocarboxylic acids from a-amino acids,11 and as a deprotecting reagent in peptide chemistry.12 Examples of the hydrofluonnation of alkenes with HF-pyridine are given in Table II. 

The system iV-halosuccinimide-hydrogen fluoride/pyridine can be used to prepare geminal chlorofluoro-, bromofluoro-, and fluoroiodo-substituted ketones and esters from the corresponding diazo compounds.35... 

A neutral diazo compound can be considered as both a nucleophile and an electrophile. Thus, it can be substituted by the combination of an electrophilic moiety and a nucleophilic moiety (X+ Nu ") (Scheme 8). In practice, the diazomethyl group is transformed to the fluoromethyl group by treatment with hydrogen fluoride/pyridine mixture (70 30 w/w) (X = H Nu = F), or to the halofluoromethyl group by addition of A-halosuccinimide in the same medium (X = Cl, Br, I Nu = F), e.g. formation of l.16 The reaction can be performed on secondary diazo alkanes, diazo ketones or diazo esters.16 90 316... 

Phenylcarbene and o-tolylcarbene (produced by laser flash photolysis of the diazo compounds) could not be directly observed in pentane at room temperature.22 Ylide formation in the presence of pyridine allowed the lifetimes of these species to be determined as 74 ns. In contrast, transient spectra of triplet mesitylcarbene were... 

Diazotization of 3-aminoisothiazolo[4,3-c]pyridine (197) with HONO gave the 3-diazonium salt (198) in good yield. Compound (198) was coupled with aromatic amines to give the diazo dyes (199) (Scheme 17) <80BRP2074565>. 

Pyridines, pyridones, and pyrones containing an amino or hydroxy group also undergo diazo coupling, nitrosation, and Mannich reactions, as do their benzenoid analogues, phenol or aniline. Such reactions take place under conditions of relatively low acidity where less of the compound is in the form of an unreactive cation. 

The heterocyclic diazo compounds such as diazopyrroles bear the same relation to diazocyclopentadiene that pyridine does to benzene. Just as pyridine is a base and forms a pyridinium ion, in acid solution, so diazopyrroles (5) form pyrrole diazonium salts (6). 

Coupling reactions with diazo compounds which are very sensitive to alkali often are most successful when pyridine is used as an acidfixing agent. This is especially true in the preparation of secondary polyazo dyes with l-amino-2-naphthol ethers or their sulfonic acids as intermediates. ... 

Not only gem-difluorides arc obtained from diazo compounds the reaction of pyridinium poly(hydrogen fluoride) [(HF) /pyridine] with diazo compounds gives the corresponding monofluoro derivatives. In the presence of a halogen source (IV-halosuccinimide), gem-fluorohalides are obtained as reaction products (see Table 9 and also Vol. ElOa, p732). ... 

Various organic solvents can be used, e.g. benzene, toluene, hexanes, acetone, acetophenone, diethyl ether. However, the substrate must be in large excess to the diazo compounds. The effect of additives has been examined. Pyridine or similar donor molecules retard the catalytic rates and decrease the optical yields. ... 

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