Halo-azides

March76 has provided a valuable summary of the work on additions of halogen azides to olefinic double bonds to provide / -halo azides (e.g. equation 52) the summary is based... 

The quest for efficient methods to prepare 2-aminohexoses prompted the first investigations based on glycals. It is generally known that trisubstituted alkenes (to which glycals are related) react with such unsymmetrical reagents as halo azides, leading in principle to a mixture of eight isomers 132-139. 

Direct introduction of HN3, or its equivalents, onto olefins constitutes an efficient and straightforward approach. Unfortunately, the most efficient reactions are multi-step sequences, such as epoxidation followed by opening with azide ions or hydroboration followed by iodination and snbstitution. Several one-step methods, such as halo-azidation, diazidation, seleno-azidation, nitrato-azidation, ° formation of a-azido ketones," and carboazidation, have also been reported, bnt the conceptually simplest reaction, the hydroazidation reaction, has been much less developed (Figure 4.1). 

The behaviour of /S-oxovinylazides is quite similar to those above. The Z isomer (556), formed from the /S-halo carbonyl compound and sodium azide, is unstable losing N2 and forming the isoxazole (557) in an anchimerically assisted concerted reaction (75AG(E)775, 78H(9)1207). At moderate temperatures (50-80 °C) the E isomer formed acylazirines which at higher temperatures rearranged to oxazoles and isoxazoles. 

Aqueous solutions of vanadous chloride (vanadium dichloride) are prepared by reduction of vanadium pentoxide with amalgamated zinc in hydrochloric acid [213], Reductions are carried out in solution in tetrahydrofuran at room temperature or under reflux. Vanadiiun dichloride reduces a-halo ketones to ketones [214], a-diketones to acyloins [215], quinones to hydroquinones [215], sulfoxides to sulfides [216] and azides to amines [217] (Procedure 40, p. 215). 

Mass fragmentation of modified nucleobases of 6-methyl tetrazolo[l,5-c]pyrimidin-5(6fl)-one and its 7 and 8-methyl derivatives suggested the occurrence of both azide and tetrazole tautomeric forms of M (661 and 662). For the 8-halo derivatives, only the of the tetrazole form was proposed (930MS643) (Scheme 135). 

Lithium diisopropylamide, 163 Phenyl azide-Aluminum chloride, 240 Halo carbonyl compounds (see also Unsaturated carbonyl compounds) a-Chloro acids Sodium nitrite, 282 a-Halo aldehydes and ketones... 

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