Triazene method

Dinitrogen tetroxide is the most versatile of the nitrosating reagents and, in addition, it is readily available. The nitro-soamide method of deamination gives far superior yields and much less skeletal isomerization than the nitrous acid method (which is essentially limited to aqueous media), and it leads to a greater retention of optical activity than the triazene method.8... 

Key reactions of the total synthesis of the vancomycin aglycon presented by Nicolaou and coworkers [4-6] are a Suzuki coupling [15] for the synthesis of the M(5-7) unit (Scheme 5) and the triazene method, described recently for the construction of macrocyclic biaryl ethers (Scheme 6) [16]. 

Reactions in which a bond from carbon to nitrogen is broken are important in several areas of organic chemistry. The Hofmann and Cope eliminations are widely used in synthetic chemistry, and the deamination of aliphatic amines (via the nitrous acid, nitrosoamide and triazene methods) has been widely studied, usually with a primary emphasis on establishing the mechanism of the reaction. Since there has been much research activity in the latter area recently, a major fraction of the chapter is devoted to an interpretive and critical review of the deamination reactions. 

Diaminobiphenyl (former name benzidine) can be easily bisdiazotized, but is not cleanly monodiazotized by reaction with one equivalent of a nitrosating agent. However, 4-aminobiphenyl-4,-diazonium ions are formed in a triazene equilibration of a 1 1 mixture of 4,4 -diaminobiphenyl with biphenyl-4,4 -bisdiazonium salts in aqueous HC1 (Tauber, 1894 see also Sec. 13.4). Methods for mono- and bisdiazotiza-tion of 1,4-diaminobenzene (/ -phenylenediamine) have been described by Saunders and Allen (1985, p. 29 see also Sec. 2.2). 

Another method of hydroxy-de-diazoniation with better yields was published by Satyamurthy et al. (1990). This method consists of the hydrolysis of l-aryl-3,3-di-ethyltriazenes in acetonitrile using a boiling mixture of the sulfonic acid resin BioRad AG 50W-X12 and water. For nine monosubstituted diethylaryl-triazenes, phenols were obtained in yields of 65-95% (Scheme 10-10). Other triazenes and the same sulfonic acid resin were also used for halo-de-diazoniations (see Sec. 10.6). 

The synthesis and mechanism of formation of a triazene from an arenediazonium ion and an amine with one or two aliphatic substituents (see Scheme 13-1, R = alkyl, R = H or alkyl) will be discussed in Section 13.2. Here we will briefly mention Dimroth s method (1903, 1905 a) for synthesis of wholly aliphatic triazenes (Scheme 13-6, R and R = alkyl). Dimroth obtained these by the action of Grignard reagents on alkyl azides followed by isolation via copper(i) salts. The Grignard method can also be applied for the synthesis of triazenes with an aromatic substituent by using an aryl azide. 

Eine vorteilhafte Methode zur Herstellung von Phenylhydrazin geht von 1,3-Diphenyl-triazen aus4 ... 

Other compounds with nitrogen-nitrogen bonds have been used instead of diazonium salts. Among these are N-nitroso amides [ArN(NO)COR], triazenes, and azo compounds. Still another method involves treatment of an aromatic primary amine directly with an alkyl nitrite in an aromatic substrate as solvent. ... 

Schmiedenkamp, A. M., I. A. Topol, S. K. Burt, H. Razafinjanahary, H. Chermette, T. Pfatzgraff, and C. J. Michejda. 1994. Triazene Proton Affinities A comparison between Density Functional, Hartree-Fock, and Post-Hartree-Fock Methods. J. Comp. Chem. 875, 875. 

A combination of the SNAr feature and the coordination ability of a copper complex has led to the development of a new O-arylation method that makes use of a triazene as an activating and directing group (Equation (2)).32,33 This protocol, though necessitating a three-step removal sequence of the triazene moiety, has been successfully applied to the total synthesis of vancomycin1 6 and extended to a solid-phase synthesis in which the triazene unit serves as an anchor to the resin.37... 

Method A The reactive haloalkane (10 mmol) is added to a stirred solution of the triazene (5 mmol) and TEBA-Cl (O.ll g, 0.5 mmol) in aqueous NaOH (50%, 20 ml) and PhH (40 ml) at 50-60°C. When TLC analysis shows the reaction to be complete (a colour change in the organic phase from red to yellow-orange is noted at the end of the reaction. ca. 10-15 min), the PhH phase is separated, washed with H20 (2 x 50 ml), and dried (MgS04). Evaporation under reduced pressure yields the alkylated product. 

Di-(o-tolyl)-triazene, om-yel crysts, mp 51°. It was first prepd in 1887 by Fischer Wimmer (Ref 1, p703 Ref 2) by reaction of 2 moles o-toluidine, 3 moles aq HC1 1 mole NaN02 soln in the presence of Na acetate and cooling. ADL (Ref 9) describes its method of prepn and gives heat of combstn Qc=1914kcal/mol at Cv... 

Solid-phase methods are applicable to syntheses of sequence-specific oligomers and dendritic structures. The triazene chemistry developed for this specific purpose may also be useful in other types of syntheses. Further development of solid-phase syntheses of this type into combinatorial synthesis of oligomers is the next logical step. Solid-phase methods will never completely replace solution-phase approaches to oligomers, but either technique should be considered with respect to the special characteristics and requirements for the system under investigation. 

Rearranged products of type R2YC = CR1R2 are obtained from the vinyl triazene 112 when R2 is an aiyl group and Rx is hydrogen or methyl and also when R2 is tolyl and Rx is phenyl. The acid-catalysed decomposition of vinyl triazene which occurs in very mild conditions has been exploited as a useful method for the synthesis of vinyl sulphonates (Jones and Maness, 1969, 1970 Modena and Tonellato 1971). 

Diaryl-, alkylaryl-, and, to a lesser degree, dialkyltriazenes are readily available. Consequently most triazenide complexes are synthesized from the free triazene or one of its salts. The salient methods, together with illustrative examples, are given below. 

Summary Graft copolymers with poly(organosiloxane) backbone and thermoplastic side chains have been synthesized via the "grafting fi om" method based on azo- and triazene modified poly(organosiloxane)s. Initiation of free radical polymerization is possible from the polymeric azo and triazene initiators after thermal decomposition of the labile frmctions in solution. The graft products have been characterized by NMR, GPC, and DSC. Stable, free standing films can be cast from the graft copolymers. 

Pyrazolylpyrimidines (pzpm) also provide a method for detecting the Pd-N bond rupture (see equation 16). This has been extended to tri-substituted triazines, wherein Pd-N bond rupture can be detected, but which also allows the metal to pass around the entire ligand via a series of (1) metallotropic shifts involving retention of the triazene N-Pd bond and (2) pyrazolyl ligand assisted metal hurdling from one triazene N to another (see equation 17). The subject of metals shuttling... 

Triazenes can be prepared by the following three methods (Scheme 1) (1) redox reactions (reduction of azides, oxidation of triazanes), (2) building or splitting of nitrogen chains, and (3) exchange of substituents (mutual transformation of triazenes). 

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