Allylic azides

The interaction of diazomethane with 1-azirines was the first example of a 1,3-dipolar cycloaddition with this ring system (64JOC3049, 68JOC4316). 1,3-Dipolar addition produces the triazoline adduct (87). This material can exist in equilibrium with its valence tautomer (88), and allylic azides (89) and (90) can be produced from these triazolines by ring cleavage. 

An explosion occurred in the final stages of evaporation of ether from allyl azide [1] Peroxides in the ether may possibly have been involved, but the azide itself is of limited thermal stability, though apparently capable of distillation at 76°C/1 bar. The vapour is weakly explosive [2],... 

Employing iminophosphoranes to protect a group labile under alkaline conditions can lead to a dramatic increase in yield. This is exemplified by the transformation of allylic azide 31 into the corresponding iminophos-phorane 32 shown in Scheme 16. Hydrolysis under basic conditions leads finally to 4-amino-3-hydroxycyclohexa-l,5-diene-l-carboxyclic acid (33) in 80% yield. However, when the same azide (31) is converted with a Lindlar catalyst, via allylic amine 34 into carboxylic acid 33, only 0-30% yields are found as a consequence of the low stability of the allylic amine [93JCR(S)148]. 

Alkyl and Aryl Azides are discussed by J.H. Boyer F.CCanter in ChemRevs 54, 1-59(1954) (See under individual compds, such as allyl-azide, phenylazide, etc)... 

The same 3-si lyl-( )-hex-4-enoates have been transformed into /-lactones 67 and 68 by asymmetric dihydroxylation (Scheme 13).[62 821 After mesylation the remaining hydroxyl was substituted by an azide with inversion of configuration. When the silane group was first eliminated to give the allyl azide 69, reduction of the latter could not be achieved. Therefore, reduction and Boc protection of the resulting amine was performed before silane elimination, to give the Boc-protected dipeptide isostere 70. 

Scheme 8E.14. Allylic azidation and synthesis of pancratistatin and epibatidine.

Based on results presented in Scheme 37, Logothetis suggested that the thermal decomposition products from the olefinic azides in the scheme are derived from triazoline intermediates formed by an intramolecular cycloaddition reaction and not by fragmentation of the azido group to a nitrene.100 However, allyl azide and 4-azido-l-pentene do not undergo internal cycloaddition because of the strain in the corresponding triazoline they fail to give aziridines and imines upon thermolysis.100... 

The possibility of cycloaddition of diazomethane to the imine bond in azirines has been investigated365,366,366 the products comprise a mixture of isomeric allyl azides, and it is possible that bicyclic triazolines are intermediates in this reaction (Scheme 103).366... 

The reactions of cyclic TIPS enol ethers with PhIO/TMSN3 (1 2) have been examined in detail [12 -14]. Two primary modes of reactivity have been identified, one leading to vicinal-diazides (a-pathway) and the other leading to allylic azides (/1-pathway) (Scheme 3). 

Synthetic applications of the /1-pathway include conversions of the TIPS allylic azides to enones with tetrabutylammonium fluoride, ionization of the C-N3 bond with alkylaluminum reagents and capture of the TIPS enonium ions with carbon nucleophiles, and development of a procedure for y-lactamization [15-17]. Allylic azidonations of TIPS enol ethers have also been incorporated into syntheses of (+)-pancratistatin [18,19] and the core structure of lycorane [20]. 

It has been shown that allylic azides can be trapped, using either phenylacetylene cycloaddition to the azide, or alkene epoxidation, and that [3,3]-sigmatropic equilibration of the possible allylic azides is generally faster than the trapping reactions 42 Nucleoside-derived azide (46) has been shown to undergo reversible [3,3]-sigmatropic... 

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... 

Logothetis first reported that azirine (24a) reacts with diazomethane to produce the allyl azide (163).68 This reaction is postulated to proceed by a 1,3-dipolar cycloaddition to form the triazoline (162) which then undergoes a valence tautomerization to the allyl azide (163). 

Dihydro-2//-pyran and related glycals underwent with PhIO-Me3SiN3 either allylic azidation or addition to the double bond trans azido adducts), depending on the conditions [94,95]. (CAUTION it has been reported that PhI(N3)2 formed in situ in the presence of moisture is explosive, even in dichloromethane solution therefore, all glassware should be flame-dried and exhaustively flushed with nitrogen). 

Steroidal alkenes, with lead(IV) azide/acetate, can yield cleaved derivatives such as (87),or its des-azido analog, or the uncleaved azido ketone,or the allylic azide, according to conditions, as well as the 1,2-diazi s mentioned earlier (Section 3.S.3.2). 

Benzeneselenenyl azide adds to alkenes readily. The addition of the selenenyl azide always occurs with trans stereochemistry. The yield of adducts is reliably high with several different alkenes. Unlike benzeneselenenyl chloride, mixtures of regioisomers are found with simple primary alkenes. No addition occurs between benzeneselenenyl azide and ethyl crotonate. The reagent adds to conjugated dienes in a trans 1,4-fashion which is thought to be due to an initial trans 1,2-addition, followed by a facile 1,3-allylic azide shift (equation 19). Unfortunately, this reagent must be prepared and used in situ ... 

The reaction of alkenes with iodosobenzene in acetic acid in the presence of sodium azide offers a simple and high yield route to 1,2-diazides (Table 3)76. a-Azido ketones are side products or the exclusive product from the reaction with conjugated alkenes. Allylic azides or oxonitriles, resulting from oxidative cleavage of the C-C double bond, are alternatively obtained from trisubstituted steroid alkenes77. 

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