Rearrangement of azides

Compound 44 has the presumed Z configuration, since it is obtained by a sterically controlled hydrolysis of the diester 43. The E configuration of 46 then follows from rearrangement of azide to isocyanate 45, which occurs with retention of configuration. 

Benzodithiazines 259 and 260 were prepared by thermally induced rearrangement of azide 258 (Equation 75) <2000JHC955>. 

The structure of the acid or the presence of substituents may affect certain steps in the Curtius reaction. Although it is usually a matter of choice whether the hydrazide method or the sodium azide method is employed for the preparation of a given azide, for certain azides one of the methods may fail completely or may be preferable because of the structure of the acid or the presence of certain groups in the molecule. As a rule the rearrangement of azides to isocyanates proceeds without difficulty. The product obtained by hydrolysis of the isocyanate is not always an amine certain isocyanates yield aldehydes or ketones. 

It should be obvious from the foregoing remarks that the rearrangement of azides in the complete absence of a solvent is highly hazardous however, it has sometimes been accomplished successfully. Catalystf... 

A third approach to 3-amino-/3-lactams is by Curtius rearrangement of the corresponding acyl azides. These are readily prepared from r-butyl carbazides, available via photochemical ring contraction of 3-diazopyrrolidine-2,4-diones in the presence of f-butyl carbazate (c/. Section 5.09.3.3.2). Thus treatment of (201) with trifluoroacetic acid followed by diazotiz-ation gives the acyl azide (202) which, in thermolysis in benzene and subsequent interception of the resulting isocyanate with r-butanol, yields the protected 3-amino-/3-lactam (203) (73JCS(P1)2907). 

The rearrangement of the azide is complete when nitrogen evolution ceases. This is usually concluded in the time indicated, but occasionally takes longer. 

The methyl ester (100, R = CH3), derived from this A-nor acid by treatment with diazomethane, is different from the ester (102) obtained either by Favorskii rearrangement of 2a-bromo-5a-cholestan-3-one (101) or by the action of cyanogen azide on 3-methoxy-5a-cholest-2-ene (103) followed by hydrolysis on alumina. The ketene intermediate involved in photolysis of (99) is expected to be hydrated from the less hindered a-side of the molecule to give the 2j -carboxylic acid. The reactions which afford (102) would be expected to afford the 2a-epimer. These configurational assignments are confirmed by deuteriochloroform-benzene solvent shifts in the NMR spectra of esters (100) and (102). ... 

Ethyl 1 -phenyl-1,8b-dihydroazirino[2,l- ]isoquinoline-3-carboxylate (2), obtained by decomposition of azide 1 (see Section 3.2.1.1.1.1.) in the presence of triethyl phosphite, on heating under reflux in toluene, rearranges quantitatively to the 3//-3-benzazepine 3.82... 

A plot depicting isokinetic relationships, (a) The thermal rearrangement of triarylmethyl azides, reaction (7-35) is shown with different substituents and solvent mixtures. The slope of the line gives an isokinetic temperature of 489 K. Data are from Ref. 8. (b) The complexation of Nr by the pentaammineoxalatocobalt(III) ion in water-methanol solvent mixtures follows an isokinetic relationship with an isokinetic temperature of 331 K. The results for forward (upper) and reverse reactions are shown with the reported standard deviations. Data are from Ref. 9. 

Rearrangement of acyl azides in the presence of water (Curtius)... 

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