Azide addition

Bromine azide addition to testosterone esters is achieved by the same procedure with the use of //-bromosuccinimide. 

The reactions of enamines as 1,3-dipolarophiles provide the most extensive examples of applications to heterocyclic syntheses. Thus the addition of aryl azides to a large number of cyclic (596-598) and acyclic (599-602) enamines has led to aminotriazolines which could be converted to triazoles with acid. Particular attention has been given to the direction of azide addition (601,603). While the observed products suggest a transition state in which the development of charges gives greater directional control than steric factors, kinetic data and solvent effects (604-606) speak against zwitterionic intermediates and support the usual 1,3-dipolar addition mechanism. 

Despite these significant results in azide additions, only limited success has been obtained in enantioselective addition of other sp2-hybridized nitrogen-centered nucleophiles to meso-epoxides. Bartoli et al. demonstrated that aniline was a... 

Nitrilium salts, e.g., 66, prepared from the alkylation of nitriles, react with sodium azide to yield 1,5-disubstituted tetrazoles, e.g., 67 (Scheme 7).121 The Schmidt reaction,122 a versatile method for the preparation of 1,5-disubstituted tetrazoles from ketones and hydrazoic acid, can now be regarded as a special case of azide addition to nitrilium salts.123... 

A reaction known as diazo group transfer produces diazo barbituric acid from barbituric acid and p-toluene sulfonyl azide. Additional barbituric acid affords azo barbituric acid [7]. Subsequent complexation with a nickel (II) salt yields a greenish yellow pigment. 

Table I contains a selection of examples of alkyl azide additions.

Beside the fact that azide addition to C50 is a convenient method for functionalizing fullerenes, the iminofullerenes also serve as precursors in the synthesis of nitrogen heterofullerenes [171]. Their chemistry is described in more detail in Chapter 12. 

Azides are easily prepared by nucleophilic substitution of alkylhalogenides with sodium azide and the yields of azide additions to CgQ are generally sufficient. Thus the functionalization of CgQ via this pathway leads to a broad range of products. Some examples are shown in Table 4.6. 

Azide ion will catalyze rearrangements of N- (aryloxy)pyridinium salts to give 3-(o-hydroxyphenyl)pyridines (Scheme 114). It is suggested that azide addition to the a-position... 

To 0.2 mole of an olefin dissolved in 30 ml of glacial acetic acid is added 19.5 gm (0.3 mole) of sodium azide in 75 ml of water. The addition to acrolein and jf -nitrostyrene underwent rapid addition, requiring cooling with an ice-salt bath and slow addition of the sodium azide. Addition to methyl acrylate, acrylic acid, and acrylonitrile required 1-3 days at room temperature, a-vinyl pyridine and mesityl oxide required heating for 24 hr on a steam bath. Other olefins underwent no reaction even after 7 days of heating and were recovered unchanged. 

Aryl azides react with olefins to give 1,2,3-A2-triazolines.201-203 Whereas unactivated olefins are sluggish toward aryl azides, strained bicyclic systems, on the contrary, are particularly reactive.204-208 The rate of phenyl azide addition to a series of olefins parallels the heat of hydrogenation (Table Vffl).107 This thermodynamic parameter is a measure for the degree of strain associated with these molecules.200 Bicyclo[2.2.1]hep-tenes, such as norbomene (37), react readily at room temperature, and the addition occurs at the less hindered exo side (39).,06 1°7 210 211 A striking example of the increased... 

Iodine isocyanate addition to olefins / 22 Halogen azide addition to olefins / 24 Via epoxides and / -mesyloxy azides / 27 By addition of alkoxyamines / 29... 

Alkynes add to azides to form 1,2,3-triazoles (equation 10). In contrast to the azide additions to alkenes, the regioselectivity with alkynes is low and usually mixtures of triazoles are formed.178 Alkynes have HOMO energy levels lower than those of the corresponding alkenes, although the LUMOs are ap-... 

There are two main approaches to the synthesis of A2-l,2,3-triazolines these involve the union of the C—C and N—N—N fragments as in the olefin-azide additions or alternately building from the C—N and C—N—N moieties as achieved through the imine-diazoalkane reactions (Scheme 2). The choice is determined by the type of substitution desired on the triazoline ring. Imines in general can be more easily prepared than the corresponding olefins. 

Although several early reviews provide brief discussions on olefin-azide additions,6-9 the greater part of the work on imine-diazoalkane reactions is more recent and not covered previously.10,11 The major methods of triazoline synthesis are outlined in a recent treatise on 1,2,3-triazoles.13... 

Unsymmetrically substituted olefins also exhibit a marked orientational specificity in azide addition reactions7,9,12,27,32 the direction of addition is controlled by electronic rather than steric factors.28 Thus unlike acetylenes,33... 

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