Azides alkylation/arylation

Diacetylenic lotsitch reagents with azides (THF, 15-18°C, 20 h) afford l-alkyl(aryl)-5-ethynyl-l,2,3-triazoles (94) in 48-70% yield(67ZOR2241). These... 

The Schmidt reaction of ketones works best with aliphatic and alicyclic ketones alkyl aryl ketones and diaryl ketones are considerably less reactive. The reaction is only seldom applied to aldehydes as starting materials. The hydrazoic acid used as reagent is usually prepared in situ by treatment of sodium azide with sulfuric acid. Hydrazoic acid is highly toxic, and can detonate upon contact with hot laboratory equipment. 

With alkyl aryl ketones, it is the aryl group that generally migrates to the nitrogen, except when the alkyl group is bulky. The reaction has been applied to a few aldehydes, but rarely. With aldehydes the product is usually the nitrile (16-21). Even with ketones, conversion to the nitrile is often a side reaction, especially with the type of ketone that gives 17-31. A useful variation of the Schmidt reaction treats a cyclic ketone with an alkyl azide (RN3) in the presence of TiCU, generating a... 

When 2-alkyl-3-keto esters or 2-aryl-3-keto esters are treated with sulfonyl azides under basic conditions, nucleophilic deacylation occurs to yield 2-alkyl/aryl-2-diazo esters [960-963]. Nucleophilic deacylation can also be used to convert acceptor-substituted diazoketones into the corresponding acceptor-substituted diazomethanes [964,965]. In all these deacylation reactions it is the most electrophilic carbonyl group which is attacked by the nucleophile and cleaved off. 

Thermolytic rearrangement of 1,2,3-trisubstituted cyclopropenyl azides constitutes the only proven method at present for the preparation of monocyclic 1,2,3-triazines, and both the generality and validity of the procedure have been established. Thus, a substantial number of derivatives of the type 2, R = alkyl, aryl, have now been prepared, and X-ray crystallographic analysis has confirmed the structures of the products (see Section II, D, 2). Thermolysis of triarylcyclopropenyl... 

RCON -+ RN = CO. The carbamoyl azides, as a group, were classified by Bertho (Ref 3) as resistant to the Curtius rearrangement. However, other work by Stolle (Ref 2) showed that while some members of this group (RL or Ra H and Ra or Ra alkyl/aryl) failed to become rearranged, others (Rt or Ra CjHs) did so. Scott et al offered a different interpretation for the resistance of carbamoyl azide to such change... 

Finally, the hydroboration-amination method via azides might be the key step in the synthesis of alkyl aryl ketones involving a free radical mechanism as opposed to the usual ionic pathway [64,65] (Scheme 23). 

For nonsymmetrical bicyclic imidazoles, direct TV-alkylation (arylation or acylation) is problematic since site-selectivity is influenced by many subtle electronic effects. Thus, Curtius rearrangement-based syntheses have been used widely for the synthesis of differentiated TV-substituted thienoimidazoles (104), (106) from (acylamido)thiophene carbonyl azides (103), (105) (Equations (30) and (31)) <79JCR(S)96>. These intermediates are useful for the synthesis of angiotensin II antagonists (Equation (32)) <91EUP483683,92EUP520423>. 

Disubstituted iminothiatriazolines may be formed by reaction of alkyl azides and aryl isothiocyanates but the reaction is relatively slow and the thiatriazoline formed undergoes further reaction with the isothiocyanate present (Section 4.28.2.3.l(iii)). 4-Alkyl-5-sulfonyliminothiatriazolines (73) are readily obtained when the more reactive sulfonyl isothiocyanates are treated with alkyl azides at room temperature (equation 47) (73JOC2916, 74JA3973). 

These compounds contain the characteristic group -N=S(0)X- (where X = Cl, F, alkyl, aryl, or R2N). Unlike the isoelectronic cyclophosphazenes, only six-membered rings have been well characterized. The sulfanuric halides are colorless solids (X = Cl) or liquids (X = F), which are stable in dry air. Sulfanuric chloride is best prepared by treatment of SOCI2 with sodium azide (equation 26). It may also be obtained as a mixture of a- and /3-isomers in a two-stage reaction from H2NSO3H and PCI5. The fluoride, [NS(0)F]3, is formed as a mixture of isomers by the fluorination of [NS(0)C1]3 with SbF3. 

The decomposition of organic azides has been studied from a number of points of view, the objectives being mainly synthetic or mechanistic. The nature of the intermediates formed have received much attention. In this chapter we shall consider the decomposition of alkyl, aryl and sulphonyl azides under various conditions. Acyl and vinyl azides are considered elsewhere in this volume. 

This present treatment is subdivided into the five major modes of decomposition acid-catalysed, thermal, trivalent phosphorus compound-catalysed, photolytic and transition metal-catalysed decompositions. Each section is further subdivided into alkyl, aryl and sulphonyl azide decomposition. The nature of the products formed and how these are affected by the nature of the reactive intermediates is discussed. 

The first step is likely to be a so-called Hieber base reaction (0 in Scheme 1), describing a nucleophilic attack at metal-coordinated carbon monoxide by hydroxide. While eq. (3) is the prototypical example as first reported by Walter Hieber in 1932 [5], several other variants have since become known. For example, azides and alkyl/aryl anions attack metal carbonyls according to eqs. (4) and (5), yielding metal isocyanates (via a Curtius-type azide degradation step) and metal carbenes, respectively [6, 7]. 

Vinyl Azides. Vinyl azides such as 37 or 38 react with alkyl-, aryl-, and heteroaryllithium reagents like other azides to give the corresponding triazenes. Hydrolysis of the latter leads to nitrogen-free carbonyl compounds when aliphatic lithium reagents are used (path A, Eq. 28),277 but when benzyl, aromatic, and heteroaromatic lithium reagents are used, amines are formed in fair to good yields (path B).278... 

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