Hydrogen chloride with arenes

Several other versions of these catalysts have been developed. Arene complexes of monotosyl-l,2-diphenylethylenediamine ruthenium chloride give good results with a,(3-ynones.55 The active catalysts are generated by KOH. These catalysts also function by hydrogen transfer, with isopropanol serving as the hydrogen source. Entries 6 to 8 in Scheme 5.3 are examples. 

The earliest catalytic application of C-H bond activation and functionalisation is that of methane using platinum chlorides as the catalyst and oxidising reagent. The exchange of hydrogen atoms in arenes with D20 was... 

Chloromethylation is a useful method for substitution of —CFI2C1 for an aromatic hydrogen, provided one starts with a reasonably reactive arene. The reagents are methanol and hydrogen chloride in the presence of zinc chloride ... 

Tandem cyclizations can also be terminated by cyclization to an arene conjugated with a carbonyl group. Oxidative cyclization of either the E- or Z-isomer of 71 with Mn(OAc)3 in acetic acid affords 72, which undergoes slow loss of hydrogen chloride to afford 79% of the desired naphthol 73 (Scheme 23) [43, 44]. Similar cyclizations were used for the first syntheses of okicenone and aloesaponol III [45]. 

Ar. hydroxylation. Triflic acid added to toluene at 0° under N2, followed by dropwise addition of bis(trimethylsilyl) peroxide in toluene, stirred for 30 min, then quenched with ice water o-hydroxytoluene. Y 88% (o m p 63 10 27). The method is fast and more convenient than reaction of H2O2 in superacidic medium or in pyridinium poly(hydrogen fluoride). With solid arenes, methylene chloride was used as solvent. F.e.s. G.A. Olah, T.D. Ernst, J. Org. Chem. 54, 1204-6 (1989) a-hydroxylation of carboxylic acids and amides following deprotonation with /-Pr2NLi s. M. Pohmakotr, C. Winotai, Synth. Commun. 18, 2141-6 (1988). 

They subsequently performed a reaction of 1-chloropentane with aluminum chloride using benzene as the solvent. Once again, they observed evolution of hydrogen chloride, but this time they found that 1-pentylbenzene ( amylbenzene ) was a major product In describing their discovery to the Chemical Society of France in 1877, they reported, With a mixture of [alkyl] chloride and hydrocarbon [an arene], the formation is established, in good yield, of hydrocarbons from the residues of the hydrocarbon less H and from the chloride less Cl. It is thus that ethylbenzene, amylbenzene, benzophenone, etc., are obtained. A general representation of the transformation is shown in the following equation. 

Vinylpyridine gives in the Meerwein reaction with arene diazonium chlorides, 2-(a-chloro-jS-arylethyl)pyridines, some of which readily lose hydrogen chloride, yielding stilbazoles ia. 2- and 3-Vinylpyridines have been used in Diels-Alder reactions with dienes37i -2 ... 

Finally, these particles generated in ionic liquids are efficient nanocatalysts for the hydrogenation of arenes, although the best performances were not obtained in biphasic liquid-liquid conditions. The main importance of this system should be seen in terms of product separation and catalyst recycling. An interesting alternative is proposed by Kou and coworkers [107], who described the synthesis of a rhodium colloidal suspension in BMI BF4 in the presence of the ionic copolymer poly[(N-vinyl-2-pyrrolidone)-co-(l-vinyl-3-butylimidazolium chloride)] as protective agent. The authors reported nanoparticles with a mean diameter of ca. 2.9 nm and a TOF of 250 h-1 in the hydrogenation of benzene at 75 °C and under 40 bar H2. An impressive TTO of 20 000 is claimed after five total recycles. 

Carboxylic acid fluorides, intermediates in the pathway to trifluoromethyl derivatives, are readily formed in reactions of all types of carboxylic acids with sulfur tetrafluoride derivatives (see Section 8.2.4.). Little attention has been paid to fluorination of other carboxylic acid halides. Aroyl chlorides are converted into aroyl fluorides by treatment with sulfur tetrafluoride, e.g. formation of l,41 or to (trifluoromethyl)arenes, e.g. 2 and 3. in the presence of hydrogen fluoride.45 Chlorination of the aromatic ring occurs in some cases.41... 

Another synthetic method involves treating the parent aromatic hydrocarbon with sodium hypochlorite in water-chloroform, using phase transfer agents like tetrabutylammonium hydrogen sulfate or benzyltrimethylam-monium chloride.15 The epoxides are formed in high yields. The rate is pH dependent, and epoxide formation is most facile at pH 8-9. Many K-region arene oxides like 1,165, acenaphthylene 1,2-oxide (19), 1-azaphenanthrene 5,6-oxide (20), 4-azaphenanthrene 5,6-oxide (21), 1,10-phenanthroIine 5,6-oxide... 

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