Diazo-donor

Another type of azides which can serve as diazo donors is the azidinium salts of the general formula 100. The important advantage... 

Tosyl azide has been used as a starting material for the synthesis of alkyl and aryl azides by acting as a diazo donor to amine metal or Grignard compounds. Yields were An example... 

Formic esters are reagents for formylation reactions. Tosyl azide is a diazo donor. 

The carbocyclic [6-7] core of guanacastepenes was prepared by. D. Trauner et al. using the intramolecular reaction between carbenoids derived from diazo carbonyl compounds and furans. The required diazo carbonyl substrate was synthesized using p-acetamidobenzenesulfonyl azide (p-ABSA) as the diazo-donor component in the Regitz diazo transfer reaction. 

In diazo transfer reactions both N-atoms, i. e., the entire diazo group, are introduced into a suitable substrate from a diazo donor (2-46). In most cases this transfer reagent is a sulfonyl azide (Y=N2 = Ar-S02N=N2 or R-S02-N=N2), from which the N(yff)- and N(y)-atoms will form the diazo group in the product. There are, however, also cases in which the diazo group of an aromatic diazonium ion or of a diazoalkene is transferred. Such examples are of minor importance. 

Diazirines are in most cases more easily available than linear diazo compounds. Moreover, their decomposition via true carbenes is free of side reactions, whereas linear diazo compounds in presence of H-donors may react by a cationic pathway. Only where reactions of linear diazo compounds are optimized for carbene formation do they give the same products as do decomposing diazirines. 

When an aprotic solvent is used, the reaction proceeds via an intermediate carbene 6. In the absence of a proton donor, a diazonium ion cannot be formed and the diazo compound 3 loses nitrogen to give the carbene 6 ... 

The most important results are given in Figure 4-1. The oxygen atom lies 244 pm from the N(l) atom of the diazonio group, well within the sum of the van der Waals radii. The diazonio group deviates by 10.4° from linearity. It seems that the 0(1) N(l) interaction is attractive, as indicated by the angle of 169.6° (instead of 180°) at N(l), but the 0(1) N(2) interaction is not. The NN distance (109.9 pm) is, however, not different from normal values found in diazonium ions. The same authors demonstrated later (Wallis et al., 1993) that this result is not unique for the quino-line-8-diazonium-l-oxide salt, as it was found also for two 1-naphthalenediazonium tetrafluoroborates substituted in the 8-position with the electron donors -SCH3 and -N(CH3)2 and - perhaps unexpectedly - for 8-nitronaphthalene-l-diazo-... 

Much earlier information on the structure of diazonium ions than that derived from X-ray analyses (but still useful today) was obtained by infrared spectroscopy. The pioneers in the application of this technique to diazonium and diazo compounds were Le Fevre and his school, who provided the first IR evidence for the triple bonds by identifying the characteristic stretching vibration band at 2260 cm-1 (Aroney et al., 1955 see also Whetsel et al., 1956). Its frequency lies between the Raman frequency of dinitrogen (2330 cm-1, Schrotter, 1970) and the stretching vibration frequency of the C = N group in benzonitrile (2255 cm-1, Aroney et al., 1955). In substituted benzenediazonium salts the frequency of the NN stretching vibration follows Hammett op relationships. Electron donor substituents reduce the frequency, whereas acceptor substituents increase it. The 4-dimethylamino group, for example, shifts it by 103 cm-1 to 2177 cm-1 (Nuttall et al., 1961). This result supports the hypothesis that... 

Aromatic diazo compounds can be reduced in water via a radical process (Scheme 11.5).108 The reduction mechanism of arenediazo-nium salts by hydroquinone was studied in detail.109 Arenediazonium tetrafluoroborate salts undergo facile electron-transfer reactions with hydroquinone in aqueous phosphate-buffered solution containing the hydrogen donor solvent acetonitrile. Reaction rates are first order in a... 

The presence of a two-electron donor ligand in the organometallic substrate that can be readily displaced by the CRR fragment of the diazo precursor is required. Alternatively, a coordinatively unsaturated species may be a suitable reactant. 

A striking feature of disperse dye development in recent decades has been the steady growth in bathochromic azo blue dyes to replace the tinctorially weaker and more costly anthraquinone blues. One approach is represented by heavily nuclei-substituted derivatives of N,N-disubstituted 4-aminoazobenzenes, in which electron donor groups (e.g. 2-acylamino-5-alkoxy) are introduced into the aniline coupler residue and acceptor groups (acetyl, cyano or nitro) into the 2,4,6-positions of the diazo component. A PPP-MO study of the mobility of substituent configurations in such systems demonstrated that coplanarity of the two aryl rings could only be maintained if at least one of the 2,6-substituents was cyano. Thus much commercial research effort was directed towards these more bathochromic o-cyano-substituted dyes. 

Methyl 3,4,5,6-tetra-0-acetyl-2-deoxy-2-diazo-D-arabino-hexonate (84) has been irradiated in methanol and in 2-propanol.177 In methanol, the only photoproduct is the enol acetate 85 however, irradiation in 2-propanol results in formation of minor proportions (6%) of 85 and the alkene 86 (7%), but the major product is the deoxy sugar 87 (61%). The difference in reactivity of 84 in these two solvents is probably a reflection of the difference in the ability of methanol and 2-propanol to function as hydrogen donors when reacting with a carbene (see Scheme 31). In methanol, a 1,2-hydrogen atom shift to the divalent... 

In summary, the chemistry of the donor/acceptor-substituted carbenoids represents a new avenue of research for metal-catalyzed decomposition of diazo compounds. The resulting carbenoids are more chemoselective than the conventional carbenoids, which allows reactions to be achieved that were previously inaccessible. The discovery of pan-tolactone as an effective chiral auxiliary, and rhodium prolinates as exceptional chiral catalysts for this class of rhodium-carbenoid intermediate, broadens the synthetic utility of this chemistry. The successful development of the asymmetric intermolecular C-H activation process underscores the potential of this class of carbenoids for organic synthesis. 

A potential problem in the use of diazo compounds as C atom precursors is the fact that intermediates in these reactions may act as C donors with the free atoms not involved. Indeed, the timing of the reactions in Eq. 6 is unknown and some of these intermediates may be bypassed in the thermolysis of 8. However, a comparison of the reactions of carbon from 8 with those of nucleogenic and arc generated carbon reveals quite similar products from many different substrates and provides circumstantial evidence for free C atoms in the decomposition of 8. 

Selectivity of Mg2+ against Ca2+ is achieved by using RO ligands such as phenoles, enolates, or hydroxide, and using nitrogen donors (e.g., 8-hydroxy-quinolinate or diazo-phenol dyes). In biology this may not be necessary as biology can control Ca2+ concentration very well. 

Ruthenium catalysts, coordinated with an N-heterocyclic carbene allowed for the ROMP of low-strain cyclopentene and substituted cyclopentenes (10,23). Suitable ruthenium and osmium carbene compounds may be synthesized using diazo compounds, by neutral electron donor ligand exchange, by cross metathesis, using acetylene, cumulated olefins, and in an one-pot method using diazo compounds and neutral electron donors (24). The route via diazo compounds is shown in Figure 1.7. 

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