A-Diazo compound

The Fuji CopiArt monochrome proofing system is based on the photogeneration of color from leuco dyes or diazo-coupling (35). CopiArt includes both positive and negative working systems (Fig. 6). For the positive working system, a diazo compound (6) reacts with a coupler (7) as shown. 

Thermal conversion of diazirines to linear diazo compounds was postulated occasionally and proved by indirect methods. The existence of a diazo compound isomeric to diazirine (197) was proved spectroscopically on short thermolysis in DMSO (76JA6416). An intermediate diazoalkane was trapped by reaction with acetic acid, yielding the ester (198) (77JCS(P2)1214). 

A final method of /3-lactam 3,4-bond formation which has found fairly wide application is based on carbenlc insertion (78T1731 p. 1739). The carbenic centre can be generated by photolysis of a diazo compound as in the case of (158) (72JA1629, 79CC846) or from organometalllc precursors, for example (159) (71ACS1927). 

The Bamford-Stevens decomposition of tosylhydrazones by base has been applied to steroids, although not extensively. It has been demonstrated that the reaction proceeds via a diazo compound which undergoes rapid decomposition. The course of this decomposition depends upon the conditions in proton-donating solvents the reaction has the characteristics of a process involving carbonium ions, and olefins are formed, often accompanied by Wagner-Meerwein-type rearrangement. In aprotic solvents the diazo compound appears to give carbene intermediates which form olefins and insertion products ... 

Reaction of tosyl hydrazone 1 with a strong base initially leads to a diazo compound 3, which in some cases can be isolated ... 

Instead of a diazonium salt, a diazo compound is obtained from reaction of a primary aliphatic amine 8 that has an electron-withdrawing substituent at the a-carbon (e.g. Z = COOR, CN, CHO, COR) as well as an a-hydrogen ... 

In the historical introduction to this book (Sec. 1.1) it was mentioned that the discoverer of diazo compounds, Peter Griess, realized quite early (1864 a) that these species could react with alkali hydroxides. Thirty years later Schraube and Schmidt (1894) found that the primary product from the addition of a hydroxide ion to a diazo compound can isomerize to form a secondary product. In this section we will discuss the equilibria of the first acid-base process of aromatic diazonium ions. In the following section additional acid-base reactions will be treated in connection with the isomerism of addition products of hydroxide ions to diazonium ions. 

If an aliphatic amino group is to a COOR, CN, CHO, COR, and so on, and has an a hydrogen, treatment with nitrous acid gives not a diazonium salt, but a diazo compound Such diazo compounds can also be prepared, often more conveniently, by treatment of the substrate with isoamyl nitrite and a small amount of acid. Certain heterocyclic amines also give diazo compounds rather than diazonium salts. ... 

There is much evidence that the mechanism" of the 1-pyrazoline reactions generally involves diradicals, though the mode of formation and detailed structure (e.g singlet vs. triplet) of these radicals may vary with the substrate and reaction conditions. The reactions of the 3 f-pyrazoles have been postulated to proceed through a diazo compound that loses N2 to give a vinylic carbene." ... 

More recently, Williams has described the one pot synthesis of 2-substituted oxazoles 11 by the thermolysis of triazole amides 9 the reaction does not proceed photo-chemically.<92TL1033> Although the reaction does not involve addition to a nitrile, it is an interesting application of a diazo compound since the proposed zwitterionic intermediate 10 is a resonance form of a diazo imine, so formally the reaction may be thought of as a thermal decomposition of a diazo imine (Scheme 6). 

Sulfonium ylides can also be generated by in situ alkylation with diazo compounds. The alkylation can be carried out by reaction of a diazo compound with HBF4 and DBU.281 The reagents are added alternately in small portions and the reaction presumably proceeds by trapping of the carbocation generated by dediazonization and deprotonation. 

If an aliphatic amino group is next to an electron-withdrawing group such as CO2R, CN, CHO, COR and has a hydrogen, reaction with aqueous nitrous acid gives a diazo compound (Eq. 11.4). Such compounds are used widely in 1,3-dipolar cycloaddition reactions, which will be covered in Chapter 12. 

The Davies group has described several examples of a rhodium-catalyzed decomposition of a diazo-compound followed by a [2+1] cycloaddition to give divinyl cyclopropanes, which then can undergo a Cope rearrangement. Reaction of the pyrrol derivative 6/2-51 and the diazo compound 6/2-52 led to the tropane nucleus 6/2-54 via the cyclopropane derivative 6/2-53 (Scheme 6/2.11) [201]. Using (S)-lactate and (R)-pari lolaclorie as chiral auxiliaries at the diazo compound, a diastereoselectivity of around 90 10 could be achieved in both cases. 

Enantioselective carbenoid cyclopropanation can be expected to occur when either an olefin bearing a chiral substituent, or such a diazo compound or a chiral catalyst is present. Only the latter alternative has been widely applied in practice. All efficient chiral catalysts which are known at present are copper or cobalt(II) chelates, whereas palladium complexes 86) proved to be uneflective. The carbenoid reactions between alkyl diazoacetates and styrene or 1,1 -diphenylethylene (Scheme 27) are usually chosen to test the efficiency of a chiral catalyst. As will be seen in the following, the extent to which optical induction is brought about by enantioselection either at a prochiral olefin or at a prochiral carbenoid center, varies widely with the chiral catalyst used. 

The outcome of the copper-catalyzed decomposition of a diazo compound in the presence of a 1,1-diarylmethanimine depends on the nature of the diazo compound. With diazodiphenylmethane, the N/H insertion product 281 and the isomeric imine... 

It has been widely accepted that the carbene-transfer reaction using a diazo compound and a transition metal complex proceeds via the corresponding metal carbenoid species. Nishiyama et al. characterized spectroscopically the structure of the carbenoid intermediate that underwent the desired cyclopropanation with high enantio- and diastereoselectivity, derived from (91).254,255 They also isolated a stable dicarbonylcarbene complex and demonstrated by X-ray analysis that the carbene moiety of the complex was almost parallel in the Cl—Ru—Cl plane and perpendicular to the pybox plane (vide infra).255 These results suggest that the rate-determining step of metal-catalyzed cyclopropanation is not carbenoid formation, but the carbene-transfer reaction.254... 

The second intermediate s identity has been debated since the mid-1980s. In 1984, Liu and Tomioka suggested that it was a carbene-alkenc complex (CAC).17 Similar complexes had been previously postulated to rationalize the negative activation energies observed in certain carbene-alkene addition reactions.11,30 A second intermediate is not limited to the CAC, however. In fact any other intermediate, in addition to the carbene, will satisfy the kinetic observations i.e., that a correlation of addn/rearr vs. [alkene] is curved, whereas the double reciprocal plot is linear.31 Proposed second intermediates include the CAC,17 an excited carbene,31 a diazo compound,23 or an excited diazirine.22,26 We will consider the last three proposals collectively below as rearrangements in the excited state (RIES). 

Direct irradiation or thermolysis of a diazo-compound (2) is believed to generate the carbene initially in its singlet spin state. Triplet sensitization (5) is presumed to give the triplet carbene directly without first forming its singlet state via the triplet diazo-compound. In some cases, careful comparison of the results of direct irradiation experiments with those from triplet sensitization can provide useful information to identify the spin state initiating a reaction. 

Lead tetraacetate, oxidation of a hydrazone to a diazo compound, 50, 7 Lithio ethyl acetate, 53, 67 Lithium, reductions in amine solvents, 50, 89 Lithium aluminum hydride, reduction of exo-3,4-dichloro-bicyclo-[3.2.l]oct-2-ene to 3-chlorobicyclo[3.2.l]oct-2-ene, 51, 61... 

C6 and C9 are at opposite ends of a four-carbon unit, but since one of these atoms (C7) is saturated and quaternary, a Diels-Alder reaction is unlikely (can t make diene). The combination of a diazo compound with Rh(II) generates a carbenoid at C9. The nucleophile 06 can add to the empty orbital at C9, generating the 06-C9 bond and a carbonyl ylide at C6-06-C9. Carbonyl ylides are 1,3-dipoles (negative charge on C9, formal positive charge on 06, electron deficiency at C6), so a 1,3-dipolar cycloaddition can now occur to join C2 to C6 and Cl to C9, giving the product. Note how a relatively simple tricyclic starting material is transformed into a complex hexacyclic product in just one step ... 

This is the first example of a direct coupling of a diazo compound in a / position of the thiophene nucleus. The Beckmann rearrangement with the ketoxime of 2-thienylketone was found to give poor yields of the aceto-2-thiopheneamide. Furthermore, the Schmidt reaction using hydrazoic and sulphuric acids was investigated and did give rise to aceto-2-thiopheneamide but probably as an eutectic with the isomeric 2-thenoylmethylamide. 

Sulfonyl azides are exceptional in that they do not normally give triazoles with activated methylene compounds nucleophilic attack by the carbanion is usually followed by loss of the sulfonamide anion, giving a diazo compound as the product. Possible mechanisms for the reaction are illustrated (Scheme 8) for diethyl malonate. Attack of the carbanion on the terminus of the azide gives the anion of the linear triazene (1). 

This automated procedure for the determination of nitrate and nitrite uses the procedure whereby nitrate is reduced to nitrite by a copper-cadmium reduc-tor column.52 The nitrite ion then reacts with sulphanilamide under acidic conditions to form a diazo compound. This compound then couples with N-1 -naphthylethylenediamine dihydrochloride to form a reddish-purple azo dye. 

Scheme 2.15 Coupling of an allenylidene ligand with a propargylic amine or a diazo-compound.

One such process involves the thermal decomposition of a diazo compound to give an acid that cross-links phenol formaldehyde resins upon heating, similar to the conventional UV initiated plates used in the industry (Figure 4.3), but other sensitisation methods are also used (see section 4.5). It is also possible to produce plates in a dry resin process by ablation or phase change methods. 

As Moody and co-workers (173) discovered, isomtinchnones can occasionally form even when they are not the desired product Thus, these workers inadvertently obtained an oxazolidinedione via an isomtinchnone rather than the desired oxoindo-line when a diazo compound was treated with rhodium(II) perfluorobutyramide in their studies leading ultimately to a synthesis of the marine alkaloid convolutamy-dine C. 

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