Benzyl azides

Whereas nitrosative decomposition of azidoalkanes such as hexyl, cyclohexyl, and benzyl azides with nitrosomum tetrafluoroborate gives only 0-5% yields of... 

The addition of benzyl azide to monosubstituted diacetylenes initially proceeds at the terminal acetylene bond to form two regioisomeric 4- and 5-ethynyl-1,2,3-triazoles 98 and 99 along with minor amounts of the corresponding diadducts (81ZOR741 82ZOR1619). 

Disubstituted diacetylenes react with benzyl azide upon long heating in toluene (12-16 h, yield 67-70%) (82ZOR1619). Comparison of the reactivity and... 

Furthermore, the ring enlargement of a range of benzyl azides was described by assuming the intermediate participation of a cyclohexadieno azirine [66]. 

To the above product, dissolved in acetonitrile, was added an equimolar amount of benzyl azide and the solution stirred under reflux for 12 h. On cooling, the precipitated product was collected, washed with ether, and dried to yield 71% of the pure product. 

Recently published examples of continuous-flow organic microwave synthesis include, for example, 1,3-dipolar cydoaddition chemistry in the CEM CF Voyager system (see Figs. 3.23 and 3.24). The cycloaddition of dimethyl acetylenedicarboxy-late with benzyl azide in toluene was first carefully optimized with respect to solvent, temperature, and time under batch conditions. The best protocol was then translated to a continuous-flow procedure in which a solution 0.33 m in both build-... 

The 1,3-dipolar cycloaddition of azides to alkynes is a versatile route to 1,2,3-tri-azoles. Different combinations of substituents on the azide and on the alkyne allow the preparation of diverse N-substitutcd 1,2,3-triazoles. Katritzky and Singh have described the synthesis of C-carbamoyl-1,2,3-triazoles by microwave-induced cydoaddition of benzyl azides to acetylenic amides (Scheme 6.220) [393]. Employing equimolar mixtures of the azide and alkyne under solvent-free conditions, the authors were able to achieve good to excellent isolated product yields by microwave heating at 55-85 °C for 30 min. In general, the triazole products were obtained as mixtures of regioisomers. Control experiments carried out under thermal (oil bath)... 

Scheme 6.220 1,3-Dipolar cycloaddition of benzyl azides with acetylenic amides.

Ethoxyvinyl trifluoromethyl ketone 243 reacts slowly at elevated temperature with aryl and benzyl azides to provide triazoles 245 in good yield (51-88%). The reactions, carried out neat, are completed usually in 2-3d(days). However, a longer reaction time (6 d) is required for 2-methylphenyl azide due to its steric hindrance. 5-Ethoxytriazolines 244, the expected intermediates in this process, readily eliminate ethanol under the reaction conditions and cannot be isolated (Scheme 34) <2002JFC(116)81 >. 

Addition of benzyl azide 56 to ester-activated cyclobutenes can be achieved under thermal conditions (no solvent, RT, several days) or better still under high-pressure (8-15 kbar, RT, DCMorTHF). 

In molecules containing two cyclobutenes, addition of organic azides 26 yielded two adducts, e.g. reaction with 50 with benzyl azide 56 produced the cr-isomer 57a in which the (V-benzyl substituents were sy -aligned and the C2-isomer 57b in which they were anti-orientated (Scheme 7). The structure of syn-isomer 57a was confirmed by X-ray (Figure 2). The fact that both isomers yielded the same fns-aziridine 58 upon photolysis made separation of the individual triazoline isomers unnecessary. 

Buchanan and coworkers71 prepared the /3-D-ribofuranosyltriazole 287 by dipolar addition of benzyl azide to the /3-d-ribofuranosylethyne 70. Related analogs have been reported by others.113a,205a,205b The anomeric 3-phenyl-4-D-ribofuranosylpyrazoles have been prepared by a dipolar, addition reaction.2050... 

Synthesis of the amino-triazole derivative (43) was performed in the authors laboratory by Pati et al. [52] (Scheme 7). Substituted benzyl bromide was reacted with triphenylphosphine to produce the phosphonium bromide starting material, 44. The Wittig reagent, obtained by treatment with sodium hydride, was reacted with 3,4,5-trimethoxybenzaldehyde 18 to generate the nitro-stilbene 45 in good yields. The alkyne 46 was obtained by bromination of the stilbene, followed by didehydrobromination. Compound 46 was then reacted under thermal conditions with benzyl azides... 

Aryl azides are converted into the corresponding anilines by polymer-supported borohydride [33]. Simple aliphatic azides are not reduced under similar conditions and the reduction of benzyl azides is slow. 

Relatively few additions of the lower molecular weight alkyl azides have been performed, mainly because of their volatility and thermal sensitivity simple alkyltriazoles are normally obtained by alkylation of the w-triazoles. On the other hand, a very wide range of less volatile substituted alkyl azides has been added to acetylenes Their addition to acetylenic esters usually proceeds readily and provides a useful method of characterizing the azides. Benzyl azide has often been used because it is relatively stable (up to 150°), it is readily prepared, and the benzyl group can be removed from the resulting triazoles (Section IV, E). 

Benzyltriazoles are readily available through cycloaddition reactions of benzyl azide. The benzyl group can be removed by reduction with... 

Cycloaddition of p-methoxyphenyl azide to alkynic dipolarophiles at room temperature gives triazoles (697) and (698) (Equation (54)). A regiospecific addition is only observed in the case of Z = CH(OMe)2 <89H(29)967>. Phenyl azide and substituted benzyl azides undergo 1,3-dipolar cycloadditions with DM AD, phenylacetylene, and ethyl propiolate to afford 1-phenyl- and 1-benzyl-... 

Warrener and co-workers (25) exploited a 1,3-dipolar cycloaddition reaction to synthesize a 7-azanorbornane 124 (Scheme 9.25). The cyclobutene-1,2-diester 121 underwent smooth cycloaddition with benzyl azide to give the triazohne 122, which... 

Formation of benzyl azide from the reaction of 1,1,4,4-tetrabenzyl-tetrazene with lead tetraacetate [70]. 

Supported carbodiimides can be produced via aza-Wittig reactions. The example in Scheme 11 shows the reaction of a benzylic azide with triphenyl-phosphine to give an aminophosphorane.31 This was then coupled with phenylisothiocyanate to give the corresponding carbodiimide. 

The presence of the aryl spacer groups, derived from the benzylic azide, in Scheme 11 was critical the reaction failed when short-chain aliphatic linkers were used. We suspect this may be due to unwanted cyclization... 

Only the 1-benzyl-vic-triazole, crysts(from eth at 20°), mp 61°, appears to have been prepd and reported in the literature. Curtius Raschig(Ref 2) prepd 1-benzyl-vic-triazole by the reaction of benzyl azide with the methyl ester of acetylene-dicarboxylic acid, followed by sapon and decarboxylation. Wiley et al(Ref 3) prepd the compd directly and in better yield from acetylenedicar-boxylic acid, followed by decarboxylation to 1 -benzyl-vic-triaZole(77% yield)... 

Perfluoro olefins combine with azides more slowly than their hydrocarbon counterparts.145 Thus benzyl azide adds slowly to perfluoropropene and -butene to give the corresponding triazolines (Scheme 29), which exhibit unusual thermal stability.145... 

Methyl ketones lead to different triazoles, depending on the azide and ketone employed (Scheme 135).2 5 s Reaction of benzyl azide with acetone and acetophenone yields mostly one or both of the triazoles derived from 38 and 39 in Scheme 64. Methyl t-butyl ketone gives, in addition, a 4-triazenyl-... 

The thermal formation of a nitrene has been invoked to account for the result in the reaction between a sterically hindered thioketene and benzyl azide437 (equation 123). Although initially a 1,3-dipolar cycloaddition between the C=S bond and the azide was expected, the temperature of the reaction (138 °C) led to decomposition of benzyl azide into benzyl nitrene and the subsequent [2 + 1] cycloaddition. 

Aube and co-workers have found that enolizable ketones react with benzyl azide in triflic acid to yield /V-(phenylamino)-methylated products [Eq. (5.354)]. The transformation is an aza-Mannich reaction interpreted with the involvement of the Mannich reagent A -phenyl iminium ion 295 formed in situ in a Schmidt rearrangement. Cyclic tertiary alcohols react with alkyl azides in triflic acid to yield N-alkylamines (296, 297)983 [Eq. (5.355)]. The Schmidt rearrangement was used to transform Merrifield resin into amino-polystyrene resin by reacting the azido derivative in excess triflic acid (CH2CI2, 0°C).984... 

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