Unsymmetrical diaryls, synthesis

Unsaturation, tests for, 360, 1058 Unsymmetrical diaryls, synthesis of, 927-928 Uramil, 851... 

Unsymmetrical diaryl sulfides (60 R = 2-NO2, 4-NO2, 2,4-(N02)2 R = H, 4-NMe2) were obtained in 80-97% yields from the reaction under PTC conditions of nitro-activated aryl halides with arenethiolates generated in situ from the reduction of the corresponding diaryl disulfides with aminoiminomethanesul-finic acid (61).192 Arylthiolates carrying electron-withdrawing substituents were not sufficiently reactive. The reaction could also be applied to the synthesis of diaryl selenides, but not of ditellurides. 

Mixed arylation of bifunctional substrates, such as those containing two /3-ketoester groups in their structure can be made. This possibility was used to synthesize unsymmetrically substituted compounds containing two different aryl groups (Scheme 2). One-pot treatment of the dibenzyl 3,7-dioxobicyclo [3.3.0]-octane-2,6-dicarboxylate 6 with a mixture of two aryllead triacetates 7 and 8 afforded a mixture of the unsymmetrical diaryl derivative 10 with the two symmetrical diaryl compounds 9 and 11. When the arylation was performed with 1.1 equiv. of each aryllead reagents 7 and 8, a mixture of 9-11 in a ratio 0.46 1 0.72 was obtained. This ratio became 0.43 1 0.49, when 0.86 equiv. of 7 and 1.33 equiv. of 8 were used. This compound 10, isolated in a 33% yield, was eventually elaborated to complete a total synthesis of ( ) methyl piperitol.25... 

Abbady MA, Hebbachy R (1993) Synthesis and application of some symmetrical and unsymmetrical diaryl sulfides and diaryl sulfones containing pyrazolinyl and isoxazolinyl moieties. Indian J Chem Sect B 32 1119-1124... 

Methyl aryl ketones can be synthesized via carbonylation of aryl iodides and tetramethyltin in the presence of a nickel catalyst (equation 14). Unfortunately the reaction cannot be extended to the synthesis of unsymmetrical diaryl ketones since tetraphenyltin does not react under these conditions. 

Sulfinate anions have been used as nucleophiles in palladium-catalyzed allylic alkylation [143]. More recently, both Cu- and Pd-catalyzed couplings of sulfinate anions with aryl halides have also been reported as a means to generate unsymmetrical diaryl sulfones, which are common motifs in bioactive molecules [38, 93, 144—148]. Similarly, Cu-catalyzed coupling of arylboronic acids with sulfinate anions has been reported [95,149,150]. Notably, Kantam and co-workers found that the use of ionic liquids permits Cu(OAc)2-catalyzed sulfone synthesis at ambient temperature and with convenient product separation and catalyst recyclability (17) [150]. 

Reproduced with permission from Mukherjee N, Chatterjee T, Ranu BC. Reaction under ballmilling solvent-, ligand-, and metal-free synthesis of unsymmetrical diaryl chalcogenides. J Org Chem 2013 78 11110-4, Copyright 2013, American Chemical Society. 

A recent application of enzyme catalysis (oxalyl chloride, 50 U aminoacylase E.C. 3.5.1.14, hexane, 4 days, 20 °C) for the synthesis of unsymmetrical diaryl ketones has been reported [949]. 

Sequential synthesis of the and anions by electrochemical reduction of the elements Se or Te provides a route to both dialky 1-di- and monoselenides and tellurides [35]. Ultrasound has also been used to promote the electrochemical synthesis of unsymmetrical diaryl chalcogenides typified by 4-phenylseleno- and -tellurobenzonitrile [228]. However, the rate enhancements observed when electrochemical reactions are exposed to ultrasound would appear to stem from the increase in mass transport rather than cavitational effects [229]. 

This aryl amination protocol was next extended to aromatic diamines. In this case, IPr was found as the best ligand and iV,iV -diarylation of aromatic diamines was obtained in high yields in 1,4-dioxane at 100 C." Diamines with spacers such as biphenyl, phenoxyphenyl or benzylbenzene were also efficiently arylated. Interestingly, the selective mono-amination of unsymmetrical diamines was obtained and therefore a two-step procedure for the synthesis of unsymmetrical -diaryl aromatic diamines could be developed. 

SCHEME 5.31 Nickel-catalyzed synthesis of unsymmetrical diaryl sulfides [47]. 

The reaction of alkyl aryl sulfides with diaryliodonium salts generated unsymmetrical diaryl sulfides in moderate to excellent yields through cleavage of the sulfur-carbon(sp ) bond and formation of a new sulfur-carbon(sp ) bond (Scheme 5.38) [60]. The synthesis was transition metal free and tolerated a host of different electron-withdrawing and donating groups. Another noteworthy aspect of the chemistry was that it was successful in an acidic environment. This renders the work complementary to the transition metal-catalyzed routes that are typically carried out under basic conditions. In related work, the... 

A closely related protocol for the synthesis of imidazoles was independently investigated by Sparks and Combs (Scheme 6.199) [362]. Here, the authors employed readily available unsymmetrical keto-oximes as building blocks, initially leading to N-hydroxyimidazoles. Diaryl keto-oximes were condensed with various aldehydes (1.1 equivalents) in the presence of 4 equivalents of ammonium acetate under microwave conditions at 160 °C. In this way, the N-hydroxyimidazoles were formed... 

The oxidative cyclization of thioacylamidines 83 is one of the best methods for the synthesis of unsymmetrical 3,5-diaryl- or dialkyl-1,2,4-thiadiazoles 84 (Equation 23) <2004HOU277>. Typical oxidants used in the cyclization step include bromine, iodine, or nitric acid, and, more recently, hydrogen peroxide in the presence of perchloric acid has been used. N-Substituted thioacylamidines give rise to 1,2,4-thiadiazolium salts <1997JOC3480>. 

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