Alkyl azides, formation

Abramovitch studied in detail photolysis of nine sec- and er -alkyl azides. Formation of imines, derived from 1,2-shifts of groups on the ipso carbon atom, was observed. 

The alkyl azide 118 is reduced to a primary amine by the Pd on carbon-catalyzed reaction of ammonium formate in MeOH at room temperature. No racemization takes place with chiral azides[l 11,112]. 

Azide ion ( N=N=N ) Sodium azide IS a reagent used for carbon-nitrogen bond formation The product IS an alkyl azide... 

The procedure described is essentially that of Shioiri and Yamada. Diphenyl phosphorazidate is a useful and versatile reagent in organic synthesis. It has been used for racemlzatlon-free peptide syntheses, thiol ester synthesis, a modified Curtius reaction, an esterification of a-substituted carboxylic acld, formation of diketoplperazines, alkyl azide synthesis, phosphorylation of alcohols and amines,and polymerization of amino acids and peptides. - Furthermore, diphenyl phosphorazidate acts as a nitrene source and as a 1,3-dipole.An example in the ring contraction of cyclic ketones to form cycloalkanecarboxylic acids is presented in the next procedure, this volume. 

Intermolecular Schmidt reactions of alkyl azides and hydroxyalkyl azides with cycloketones in the presence of a Lewis acid, lead to formation of iV-alkyl lactams and A-hydroxyalkyl lactams respectively in good yield. The synthesis of chiral lactams by an asymmetric Schmidt reaction has also been reported. ... 

The synthesis and mechanism of formation of a triazene from an arenediazonium ion and an amine with one or two aliphatic substituents (see Scheme 13-1, R = alkyl, R = H or alkyl) will be discussed in Section 13.2. Here we will briefly mention Dimroth s method (1903, 1905 a) for synthesis of wholly aliphatic triazenes (Scheme 13-6, R and R = alkyl). Dimroth obtained these by the action of Grignard reagents on alkyl azides followed by isolation via copper(i) salts. The Grignard method can also be applied for the synthesis of triazenes with an aromatic substituent by using an aryl azide. 

The direct formation of A-substituted phthalimides from phthalic anhydride and alkyl azides, via the intermediate RN=PPh, compound, is catalysed by the presence of tetra-n-butylammonium cyanide [34],... 

The same type of product was isolated from the reaction of the iminoborane alkyl azides R N3 (R = Me, Et, Pr, Bu, iBu, sBu, ra-CsHu, cyclo-CsHg, cyclo-CgHn, Ph(3H2) (19). The azidosilane Me3SiN3 may also behave as a 1,3-dipole [Eq. (40b)], but addition of the SiN bond to iminoboranes [Eq. (40a)] is usually the preferred reaction (Section V,C,8). This is not so when Me3SiN3 is present during the formation of diaryliminoboranes, ArB NAr, as intermediates Both reaction pathways [Eqs. (40a) and (40b)]... 

The introduction of two [5,6]-aza bridges shows a remarkable regioselectivity even if segregated alkylazides are used [17]. The diazabishomofullerenes 23 (Scheme 10.3) are by far the major products and only traces of one other bisadduct with unidentified structure are found if, for example, a twofold excess of azide is allowed to react with CgQ at elevated temperatures [17]. To obtain clues on the mechanism of this most regioselective bisadduct formation process in fullerene chemistry a concentrated solution of an azahomofullerene precursor 24 was treated with an alkyl azide at room temperature. 

Preparation of alkyl azides The azide ion (N3 ), a good nucleophile, can displace leaving groups from 1° and 2° alkyl halides. Alkyl azides are easily prepared from sodium or potassium azides and alkyl halides. The reaction mechanism resemhles the formation of nitrile. 

Unsubstituted alkyl azides react with nitrosonium tetrafluoroborate without formation of alkyl fluorides, but azidonitriles give fluoronitriles with this reagent.69 Depending on the chain length, rearrangements can occur extensively. Interaction between the nitrile group and boron trifluoride has been invoked to explain these reactions. 

Kreher and Jager have studied the aluminum chloride catalyzed decomposition of azidoformates in several solvents.18118 They reasonably assumed that the decomposition process in n-hexane and nitromethane solution proceeds by C02 elimination and the formation of alkyl azides which then decompose into imines (eq 5). Furthermore, infrared analysis has shown that the catalyst is fixed at the carbonyl group of the azido-formate. 

This reaction may involve stepwise addition of the two equivalents of PhNCS via a 3-membered ring intermediate, RN—S—C=NPh.66 A thia-ziridine was also suggested by Borsche67 to explain the formation of 4-phenyl-5-phenylimino-l,2,4-dithiazolidine-3-thione from the aluminum chloride-catalyzed decomposition of phenyl azide in carbon disulfide. If a 4-substituted thiatriazoline is formed from phenyl isothiocyanate and the alkyl azide, the reaction may then be formulated as indicated in Eq. (21). This scheme is supported by the recent findings of Neidlein and... 

The [2+3] cycloaddition of methylidene borane 36 with alkyl azides furnishes the intermediate triazaboroles 37a, which further undergoes silicon migration from carbon to nitrogen resulting in the formation of 37b. The driving force for the reaction is the stabilization of the ring system due to aromatization (6rt electrons) (Scheme 4) <2004ZFA508>. 

Alkyl azides readily undergo 1,3-dipolar cycloaddition to arylsulfonyl isothiocyanates (375) to yield thiatriazolines (376). Thermolysis of (376) in the presence of isocyanates or carbodiimides produces 1,2,4-thiadiazole derivatives (378) and (379), respectively. The intermediate formation of a thiaziridinimine (377) has been postulated as indicated in Scheme 137 (75JOC1728, 75S52). The use of isothiocyanates as dipolarophiles produces dithiazolidines (380) instead of the thiadiazole derivatives. In these reactions the intermediate thiazirine (377) functions as a 1,3-dipole with the positive charge primarily localized on sulfur. It was recently proposed that the reaction of oxaziridines (381) with isothiocyanates produces a similar thiazirine intermediate (382) which reacts in a different regiospecific manner with isothiocyanates to produce 1,2,4-thiadiazole derivatives (383) and (384 Scheme 138) (74JOC957). 

Acyl isothiocyanates react with alkyl azides, presumably to give the primary products (45) which have not been isolated so far (equation 20). Reaction of (45) with a second mole of acyl isothiocyanate affords 1,2,4-dithiazolidine (46) and 1,2,4-thiadiazole (47). The formation of these products may be rationalized along the same principles as discussed above (79BSB245). 

The reaction of trialkylboranes with A-chloro- or A-(benzoyloxy)alkylamines afforded secondary amines via an anisotropic 1,2-shift of the alkyl group from boron atom to nitrogen in the B-N complex intermediate.519-521 Alkylation of A-chlorodimethylamine with primary trialkylboranes to give A,A-dimethylalkylamines was conducted in the presence of galvinoxyl to avoid the formation of alkyl chlorides via free radical process.522,523 A convenient approach to mixed secondary amines is alkylation of alkyl azides with relatively unhindered trialkylboranes in refluxing xylene followed by hydrolysis with water. The reaction smoothly took place at low temperature when trialkylboranes were replaced by alkyl(dichloro)boranes (Equation (108)).524 Intramolecular amination furnished cyclic amines (Equation (109)).400,525-528... 

Formation and Reduction of Azides Azide ion ( N3) is an excellent nucleophile that displaces leaving groups from unhindered primary and secondary alkyl halides and tosylates. The products are alkyl azides (RN3), which have no tendency to react further. Azides are easily reduced to primary amines, either by LiAlH4 or by catalytic hydrogenation. Alkyl azides can be explosive, so they are reduced without purification. 

Similarly to the reaction with diazomethane, [3 + 2] cycloaddition of alkyl azides to C70 affords three constitutionally isomeric adducts (87, 88, and ( )-89) 46.226,227 Thermal elimination of N2 from the fullerene-fused triazolines showed a preference for the formation of 6-5 open azahomofullerene structures (types 90 and ( )-91) as compared to the 6-6 closed aziridine isomers corresponding to 92 and 93 (Scheme 1.9).226,227... 

Simple alkyl azides are quite labile even at room temperature and have a tendency to detonate on rapid heating for these reasons, the majority of kinetic studies have been confined to the solution phase. As with azocompounds, the common nitrogen elimination reaction is the consequence of the relative stability of the resulting, divalent RN radical, called a nitrene, and the high heat of formation of the N2 molecule. In some cases, particularly in the thermolysis of aryl azides, Nj elimination follows a concerted path nevertheless, nitrene formation is of more common occurrence in both the photolytic and thermal decompositions. Decomposition and addition reactions of organic azides have been recently reviewed . 

Azide formates and acyl azides decompose at substantially lower temperature than do alkyl and aryl azides, owing to a decrease in the double bond character of the N-N2 bond as a result of conjugation between the carbonyl and triazo groups. Acyl azides, in particular decompose at or slightly above room temperature and in some cases a concerted mechanism has been proposed , viz. 

More recently published ideas include the formation of solid derivatives of alkyl azides by treatment with acetylene dicarboxylic acid to form 1-alkyl-triazole-4,5-dicarboxylic acids. These frequently form hydrates with poor melting points and generally poor analytical properties. Alternatively, one can obtain bicyclic fused-ring triazolines by treatment with norbornadiene or dicyclopentadiene °. 

Photolysis of the aryl-alkyl azide CH CPhaNa showed that the migratory aptitudes of the methyl and phenyl groups were almost identical and this and the formation of triphenylmethyl amine from irradiation of triphenylmethyl azide in the presence of efficient hydrogen donors were taken to confirm the existence of discrete nitrene intermediates. Although the occurrence of a triplet-sensitized decomposition from alkyl azides and triphenylmethyl azides (the... 

In analogy with HN3 the decomposition of the alkyl azides is believed to go through a singlet state. In the gas phase photolysis of methyl azide the primary step is the formation of methyl nitrene ... 

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