Rearrangement allylic azides

It has been found that the thermodynamic ratio of isomeric allylic azides, interchangeable by stereoselective [3,3]-sigmatropic rearrangement, can be affected by steric and electronic factors in the presence of a bulky (chiral) auxiliary. Under Mit-sunobu conditions, treatment of allylic alcohols (48 R Ph) was shown to give a... 

Basic hydrolysis of the allylic azide affords the rearranged 1,2-isomer, which was an intermediate in the synthesis of (+)-conduramine E. Following a similar strategy, but starting with dr-3,6-dibenzoyloxycyclohex-l-ene, a total synthesis of the nonopioid analgesic (—)-epibatidine was developed. ... 

Simple allylic azides undergo rearrangement at moderate temperatures. For pentenyl and butenyl azides the forward and backward reactions follow first order kinetics and the rate is insensitive to methyl substitution or the nature of the solvent . Significantly in pentane, ether and 70 % acetone, AS = —10 and — 11 eu for a,a-dimethyl and y,y-dimethyl allylazides, respectively, and cyclic intermediates were proposed, viz. 

AUyl compounds are highly reactive towards nucleophiles and examples of dissociative (5 1) and associative (5 2) reactions, and nucleophilic substitution with rearrangement are well documented . Differentiation between these mechanisms when azide ion is the nucleophile is cften extremely difficult due to the possibility of rearrangement of the allylic azide resulting from substitution, and for this reason the relative nucleophilic strength of azide ion in allylic 5n reactions has not been delineated. 

Aliphatic azides undergo a little known allylic-type rearrangement (reaction 81). This has been studied in a variety of solvents for R = metliyl and hydrogen and the percentages of the isomers at equilibrium have been measured In contrast to the analogous iso-merizations of allylic chlorides the rates of rearrangement are insensitive both to alkyl substitution and to solvent and no accompanying... 

Isomerizations of allylic azides also appear to involve concerted, non-ionic rearrangements. Butenyl and pentenyl azides isomerize slowly at room temperature in a variety of solvents, viz. 

Scheme 13.11 Claisen rearrangement of equilibrating allylic azides.

Equilibrating mixtures of allylic azide-containing allylic alcohols or allylic 2-tolylsulfonylacetic esters undergo Johnson-Claisen or Ireland-Claisen rearrangement to give unsaturated y-azido esters and acids, respectively (Scheme 8). ... 

Allylic fra i-l,2-azidohydrins prepared by Lewis-acid-catalysed ring opening of cyclic vinyl epoxides with sodium azide via an 5 2 mechanism have been found to isomerize to trans-l,4-azidohydrins via a suprafacial allyl azide [3,3]-sigmatropic rearrangement (Scheme 16). ... 

The allylic azide 70 has been sythesized in high e.e. by treating the meso-carbonate 71 with trimethylsilyl azide in the presence of Pd and a chiral phosphine ligand as catalyst. Compound 70 was further converted to (+)-conduramine E by use of a reaction involving a [3,3] sigmatropic rearrangement. ... 

Intramolecular reactions including rearrangements such as the Overman rearrangement or rearrangement of allylic azides, and reactions of non-allylic trichloro-(fluoro)acetimidates, carbamates, etc. 

Azide salts are a class of versatile nitrogen nucleophiles that can be readily employed as reaction partners in palladium-catalyzed allylic displacement reactions. A telling example was documented by Trost in the desymmetrization of bis-carbonate 51 to give azide 52 in an excellent 95% ee (Scheme 14.10) [66]. The fact that the reaction proceeds under mild conditions ensures that any undesired rearrangement of the allylic azide 52 is suppressed. 

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