Irradiation alkyl chlorides

Keywords alkyl chloride, trialkyl phosphite, alumina, microwave irradiation, Arbuzov rearrangement, dialkyl alkylphosphonate... 

Alumina (A1203, neutral, 2 g) was added to a mixture of trialkyl phosphite (2.5 mmol) and the alkyl chloride (2 mmol). This mixture was irradiated by microwave for 5-10 min. The reaction mixture was washed with CH2CI2 (200 mL), dried (CaCI2), and the solvent evaporated to give the crude products. Pure product was obtained by distillation under reduced pressure in 73-90% yields. 

Oxime esters of aryl and alkyl carboxylic acids are apparently better substrates. These compounds decompose under irradiation, in presence of CC14, to yield aryl and alkyl chlorides in high yields (equation 70)597 ... 

In non-polar solvents such as alkanes and alkyl chlorides (RX), ionizing irradiation produces metastable parent radical cations of high reactivity [Eq. (1)]. Usually, these species decay by neutralization, deprotonation and fragmentation. At room temperature such parent radical cations exhibit lifetimes up to 200 nanoseconds. In the presence... 

The ABC ring system of the carbocyclic skeleton of variecolin, a sesterterpenoid natural product was accomplished by G.A. Molander and co-workers. In their approach, they utilized two samarium diiodide mediated processes. First, a primary alkyl iodide was reacted with a ketone substrate in the presence of two equivalents of samarium diiodide and catalytic nickel(ll) iodide under samarium Grignard conditions. Subsequent oxidation and lactone formation provided the chlorolactone substrate. As alkyl chlorides are less reactive than alkyl bromides and iodides, the second samarium diiodide mediated process, an intramolecular nucleophilic acyl substitution, required visible light irradiation. 

Samarium diiodide when coupled with irradiation is a very reactive reducing reagent with respect to alkyl chlorides, whose oxidation potential is higher than those of the corresponding bromides and iodides. When such a reduction of an alkyl chloride was attempted under CO pressure [60], an unsymmetrical ketone was obtained, comprised of two molecules of alkyl chloride and two molecules of carbon monoxide. An a-hydroxy ketone, obtained via the dimerization of acylsa-marium, is a likely precursor of the final product. 

Rate enhancement can also be achieved by irradiation of visible light.237 The polymerization of MMA with I-17/CuCl/L-l in toluene at 80 °C in the dark ceased around 40% conversion, but under irradiation of visible light, the polymerization became quantitative. This is due to a photochemical effect on the inner-sphere complex between the catalyst and the dormant alkyl chloride. 

First, upon irradiation, alkyl cobaloximes react with trichloromethanesulphonyl chloride, at 10 °C. A new carbon-sulphur bond is formed and the alkanesulphonyl chloride is produced in excellent yield546 (equation 141). 

In alkyl chlorides, bromides, and iodides the carbon-halogen bonds (C—X) are weaker than either the C-C or the C-H bonds. During irradiation mostly carbon—halogen dissociation occurs forming alkyl radical and X or X (Spinks and Woods 1990). Reaction (O 23.90) is due to the high electron affinity of Cl, Br, and I atoms, 3.61, 3.36, and 3.06 eV, respectively. 

Alkanes react with chlorine (CI2) or bromine (Br2> to form alkyl chlorides or alkyl bromides. These halogenation reactions take place only at high temperatures or in the presence of light. (Irradiation with light is symbolized by hv.)... 

The structures of aryl pyrogallol [4] arenes were confirmed by characterization of their acylated derivatives. Under microwave irradiation, alkylation reactions of aryl pyrogallol[4]arenes with some alkylating reagents such as n-butyl iodide, benzyl chloride, and ethyl a-chloroacetate were completed quickly to yield fully 0-alkyl-ated products. The H NMR spectra and crystal structures showed that the acylated and alkylated aryl pyrogallol [4]arenes existed mainly in rctf(cis-trans-trans) configuration (Yan et al., 2007). 

Alkyl chlorides have been little studied because they absorb only at very short wavelengths. However, they form charge-transfer complexes with alcohols and amines that absorb at more accessible wavelengths. Irradiation of alkyl chlorides in the presence of amines is discussed above. Direct irradiation of 1-chloroadamantane (41c) and -norbornane (8c) in alcoholic solvents afforded ethers 43a-b and 10 with quantum yields of 0.9-1.4 x 10 and 1.5 x 10 , respectively, in unstated chemical yields.Extended irradiation of (lil,2S,5i )-menthyl chloride (212) in CH3OH afforded ether 213 in unstated yield. Interestingly, the 1R,2S,5R isomer was the only observed substitution product, although the C-5 epimer was apparently not specifically looked for. 

In a typical reaction, a series of C - O linked pyrazinone-triazoles were irradiated with an excess (3.5 equiv) of DMAD in o-DCB. The reactions were completed in 6-20 min at 180 °C, using a maximum irradiation power of 200 W. After spontaneous elimination of the corresponding isocyanate or cyanogen chloride, the pyridines and pyridinones were formed in combined yields of 71-99%. It is noteworthy that the pyrazinones with an aryl moiety at the N-1 position yielded pyridines as major products, while those with ben-zyUc or alkyl ester moieties at the N-1 position furnished the corresponding pyridinones as major products. 

Alternatively, esterification of carboxylic acid can be carried out in aqueous media by reacting carboxylic acid salts with alkyl halides through nucleophilic substitutions (Eq. 9.10).20 The reaction rate of alkyl halides with alkali metal salts of carboxylic acids to give esters increases with the increasing concentration of catalyst, halide, and solvent polarity and is reduced by water. Various thymyl ethers and esters can be synthesized by the reactions of thymol with alkyl halides and acid chlorides, respectively, in aqueous medium under microwave irradiation (Eq. 9.11).21 Such an esterification reaction of poly(methacrylic acid) can be performed readily with alkyl halides using DBU in aqueous solutions, although the rate of the reaction decreases with increasing water content.22... 

Acyl hydrazides are useful precursors for the synthesis of 1,2,4-triazoles. Reaction of acyl hydrazides 149 with imidoylbenzotriazoles 148 in the presence of catalytic amounts of acetic acid under microwave irradiation afforded 3,4,5-trisubstituted triazoles 150 <06JOC9051>. Treatment of A-substituted acetamides with oxalyl chloride generated imidoyl chlorides, which reacted readily with aryl hydrazides to give 3-aryl-5-methyl-4-substituted[ 1,2,4]triazoles <06SC2217>. 5-Methyl triazoles could be further functionalized through a-lithiation and subsequent reaction with electrophiles. ( )-A -(Ethoxymethylene)hydrazinecarboxylic acid methyl ester 152 was applied to the one-pot synthesis of 4-substituted-2,4-dihydro-3//-1,2,4-triazolin-3-ones 153 from readily available primary alkyl and aryl amines 151 <06TL6743>. An efficient synthesis of substituted 1,2,4-triazoles involved condensation of benzoylhydrazides with thioamides under microwave irradiation <06JCR293>. 

A related example involves the N-alkylation of azaheterocycles such as imidazole (Scheme 4.8). These reactions are typically performed using 1.5 equivalents of the alkyl halide and a catalytic amount of tetrabutylammonium bromide (TBAB). The reactants are adsorbed either on a mixture of potassium carbonate and potassium hydroxide or on potassium carbonate alone and then irradiated with microwaves (domestic oven) for 0.5 to 1 min. With benzyl chloride, a yield of 89% was achieved after 40 s [18]. 

The soluble polymer support was dissolved in dichloromethane and treated with 3 equivalents of chloroacetyl chloride for 10 min under microwave irradiation. The subsequent nucleophilic substitution utilizing 4 equivalents of various primary amines was carried out in N,N-dimethylformamide as solvent. The resulting PEG-bound amines were reacted with 3 equivalents of aryl or alkyl isothiocyanates in dichloromethane to furnish the polymer-bound urea derivatives after 5 min of micro-wave irradiation (Scheme 7.75). After each step, the intermediates were purified by simple precipitation with diethyl ether and filtration, so as to remove by-products and unreacted substrates. Finally, traceless release of the desired compounds by cyclative cleavage was achieved under mild basic conditions within 5 min of micro-wave irradiation. The 1,3-disubstituted hydantoins were obtained in varying yields but high purity. 

N-Ethylaniline was alkylated by reaction with benzyl chloride under liquid-liquid PTC conditions in the presence of 30% sodium hydroxide solution and CTAB as a catalyst. Microwave irradiation (25 min) of the reaction mixture in a sealed vessel afforded N-benzyl-N-ethylaniline in 90% yield, compared with 16 h of conventional heating (oil bath) (Eq. 30) [24]. 

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