Alkyl azides halide displacement

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. 

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. 

A better method for preparing primary amines is to use the azide synthesis, in which azide ion, is used for 8 2 displacement of a halide ion from a primary or secondary alkyl halide to give an alkyl azide, RNj. Since alkyl azides are not nucleophilic, overalkylation can t occur. Reduction of the alkyl azide, either by catalytic hydrogenation over a palladium catalyst or by reaction with LiAlH4, leads to the desired primary amine. Although the method works well, low-molecular-weight alkyl azides are explosive and must be handled carefully. 

Organoazides. Alkyl azides are obtained by a displacement reaction of alkyl halides by using the McjSiNj-Bu jNF reagent system. 2-Azidoimidazoles are obtained from the corresponding bromo derivatives in a reaction catalyzed by (PhjPjjPdClj. ... 

The reaction of alkoxides with alkyl halides or sulfonates is a useful method for ether synthesis (entries 6-10). Disubstituted sulfides are prepared by reaction of alkyl thiolates with alkylating agents under typical Sn2 reaction conditions (entries 12 and 13). Many small anions can be introduced into organic molecules by nucleophilic substitution. Entries 15 and 16 illustrate the preparation of a nitroal-kane and an alkyl azide, respectively, by displacement reactions. The alkylation of tertiary amines to give quaternary ammonium salts is another example of a synthetically useful nucleophilic substitution process. 

Typical conditions for these processes are simply to stir an aqueous solution of the metal salt of Y with the organic substrate alone, or in a solvent such as chloroform or benzene, in the presence of 5—10 mole % of a quaternary ammonium salt as catalyst. A recent example is to be found in a synthesis of alkyl azides from alkyl iodides (or other halides) using commercially available Aliquat 336 [mainly (1)] as catalyst, and a reaction temperature of 100 °C. The conversion of alkyl methanesulphonates to alkyl halides has been used to synthesize optically active secondary fluorides, chlorides and bromides via an 5 n2 inversion mechanism (the iodides racemize before isolation). Ammonium salt (1), or phosphonium salt (2), are used to catalyse these mesylate displacements. ... 

Asymmetric introduction of azide to the a-position of a carbonyl has been achieved by several methods. These include amine to azide conversion by diazo transfer,2 chiral enolate azidation,3 and displacement of optically active trifluoromethanesulfonates,4 p-nitrobenzenesulfonates,5 or halides.6 Alkyl 2-azidopropionates have been prepared in optically active form by diazo transfer,2 p-nitrobenzenesulfonate displacement,5 and the Mitsunobu displacement using zinc azide.7 The method presented here is the simplest of the displacement methods since alcohol activation and displacement steps occur in the same operation. In cases where the a-hydroxy esters are available, this would be the simplest method to introduce azide. 

Alkyl and aryl azides are prepared by the nucleophilic displacement by azide ion on halide, sulfate, phenyldiazonium, hydroxyl, nitrate, iodoxy, alkoxy, and tosylate groups [6]. Sodium azide is the most useful and practical reagent. The use of silver azide is not necessary in most cases. Some examples from the literature [8-33] employing these methods are shown in Table I. 

A one-pot PTC reaction procedure for the overall conversion of an alkyl halide into a primary amine via an azide is particularly illustrative.204 Thus the reduction of the azide is effected by the addition of sodium borohydride to a reaction mixture arising from the PTC displacement reaction of an alkyl halide with sodium azide (the preparation of 1-octylamine, Expt 5.193). The reaction appears to be applicable to primary and secondary alkyl halides, alkyl methane-sulphonates and benzylic halides. 

To convert an alkyl halide (or alcohol, via the tosylate) to an amine, form the azide and reduce. To convert it to an amine with an additional carbon atom, form the nitrile and reduce. In either case, the alkyl group must be suitable for Sn2 displacement. 

The halogen end group can be transformed into other functionalities by means of standard organic procedures, such as a nucleophilic displacement reaction. Different authors have investigated this process of the nucleophilic displacement reactions with model compounds, to confirm the feasibility and selectivity. Compounds such as 1-phenylethyl halide, methyl 2-bromopropionate, and ethyl 2-bromoisobutane mimic the end groups of PSs, poly(alkyl acrylates), and poly(alkyl methacrylates), respectively. Different compounds have been tested, such as sodium azide, n-butylamine, and n-butylphosphine. 

In addition to the usual substitution reactions directly on the nitrogen atom of the amino or amido group, there are (as noted earlier, e.g.. Table 7.7) substitution reactions with other nucleophiles that can be converted to the amino (or substituted amino) group. These include incorporation of the azido function (produced by, e.g., a nucleophilic substitution reaction of azide anion [Ns"] on an alkyl halide) and its subsequent reduction (with lithium aluminum hydride, LiALH,) (Equation 10.60) or triphenylphosphine [( 5115)3 ] (Equation 10.61) to the corresponding amine, as well as a similar displacement reaction with isocyanate (0=C=N ) (Equation... 

Both alkyl and alkenyl amino acids can be prepared by this approach. A common method for introducing the halide into an alkene-bearing molecule is illustrated by the reaction of -pent-2-enoic acid with N-bromosuccinimide to form 1.12. Subsequent treatment with ammonia led to displacement of the bromine moiety to give 4-aminopent-2-enoic acid (J.I3). An alternative method reacted 1.12 with sodium azide and then reduced the azide with zinc and acetic acid (see section l.l.B.iv). Allylic halogenation in systems such as 1.12 are well known. 

Ionic liquids (IL) can be used as solvents for nucleophilic substitution reactions of alkyl halides or tosylates with NaN3. ° The authors studied three ionic liquids (84 and 85), [bmim][PF6], [bmim][N(Tf)2]> [hpyr][N(Tf)2] (where bmim = l-butyl-3-methyl-imidazo-lium, hpyr = 1-hexylpyridinium, PFg = hexafluorophosphate, N(Tf)2 = bis(trifluoromethy lsulfonyl)imide). It was observed that nucleofugacity scales for this reaction are similar to those reported for the same process in cyclohexane. It was also observed that elimination reaction does not compete with substitution even in cases with sterically hindered substrates such as the triflate ester of diacetone-D-glucose 81. The nucleophilic displacement on n-octyl mesylate (86) with potassium azide in a biphase system of supercritical carbon dioxide (SCCO2) and water, in the presence of catalyst Bu4PBr is also an adequate medium for the synthesis of the corresponding azide 87 ° (Scheme 3.11). 

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