Symmetrical diaryl ether

By using this mild and versatile methodology, symmetrical diaryl ethers have been synthesized in a one-pot, two-step procedure starting from arylboronic acids and their partial conversion to the corresponding phenols by oxidation with hydrogen peroxide and a subsequent coupling of the formed phenols with the remaining arylboronic acids upon addition of copper(II) acetate, molecular sieves and triethyl amine (Scheme 7) [22],... 

J. Simon, S. Salzbrunn, G. K. S. Prakash, N. A. Petasis, G. A. Olah, Regiose-lective conversion of arylboronic acids to phenols and subsequent coupling to symmetrical diaryl ethers, Journal of Organic Chemistry 2001, 66, 633. 

The mem-dichlorobenzene complex reacts with protected 0-aryltyrosines to give aryl ethers. Both chlorine atoms can be sequentially substituted to give symmetrical or disymmetrical triaryl diethers (Scheme XVI). The building up of such diaryl ethers from phenolic compounds which have amino groups in their side chains... 

Symmetrical diaryl sulfides were produced in fair yield from the PTC reaction of sodium sulfide with molten aryl chlorides activated by a cyano, nitro, phthalimido or anhydrido group.193 Typical conditions require use of a 3 1 mole ratio of aryl chloride to Na2S and 10% of catalyst (crown ethers and onium salts) at 200 C for 24 h. 

Total synthesis of a selective thyromimetic SK FL-94901 (76) was accomplished by diaryl ether formation from symmetrical or unsymmetrical diaryliodonium salts. 

A large scale synthesis of SK FL-94901 (76), which is a novel, selective, and potent thyromimetic, was established by construction of the hindered diaryl ether moiety via symmetrical iodonium salt 169 [131] (Scheme 39). 

A large number of symmetrical diaryl- or dialkyl-acetaldehydes, difficult to obtain by other means, have been prepared by the reaction of ethyl ethoxyacetate, or ethyl phenoxyacetate, with Grignard reagents followed by treatment of the resulting glycol monoalkyl ether with anhydrous oxalic acid or dilute sulfuric acid. The yield in the first step is 40-80%, and the yield in the subsequent transformation is 50-80%. 

Aliphatic nitriles react slowly with phenols and phenyl ethers in the presence of trifluoromethanesulphonic acid to give ketones after hydrolysis, in a variation of the Houben-Hoesch reaction. The crystalline complex of copper(i) triflate and benzene induces the acylation of aromatic substrates with selenol esters, affording a transition-metal mediated version of the Friedel-Crafts reaction. Aromatic carboxylic acids can be converted into symmetrical diaryl ketones in good yield by treatment of their 5-(2-pyridyl)thioesters with bis-(l,5-cyclo-octadiene)nickel [equation (15)]. In contrast to other methods for preparing symmetrical aromatic ketones, this method allows their preparation from a single starting material. 

Couladouros, E.A., Moutsos, V.I., and Pitsinos, E.N. (2003) Synthesis of o-brominated diaryl ethers using symmetrical iodonium salts application to the synthesis of bastadin precursors. ARKIVOC, 92-101. 

Nucleophilic displacement of chlorine, in a stepwise manner, from cyanuric chloride leads to triazines with heteroatom substituents (see Section 6.12.5.2.4) in symmetrical or unsymmetrical substitution patterns. New reactions for introduction of carbon nucleophiles are useful for the preparation of unsymmetrical 2,4,6-trisubstituted 1,3,5-triazines. The reaction of silyl enol ethers with cyanuric chloride replaces only one of the chlorine atoms and the remaining chlorines can be subjected to further nucleophilic substitution, but the ketone produced from the silyl enol ether reaction may need protection or transformation first. Palladium-catalyzed cross-coupling of 2-substituted 4,6-dichloro-l,3,5-triazine with phenylboronic acid gives 2,4-diaryl-6-substituted 1,3,5-triazines <93S33>. Cyanuric fluoride can be used in a similar manner to cyanuric chloride but has the added advantage of the reactions with aromatic amines, which react as carbon nucleophiles. New 2,4,6-trisubstituted 1,3,5-triazines are therefore available with aryl or heteroaryl and fluoro substituents (see Section 6.12.5.2.4). 

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