Ethers coupling

The anodic coupling of aryl ethers is reviewed in Ref. [180]. Aryl ethers are more selectively coupled than phenols for the following reasons The carbon-oxygen coupling is made impossible and the ortho-coupling and the oxidation to quinones become more difficult. A mixture of triflu-oroacetic acid (TFA) and dichloromethane proved to be the most suitable electrolyte [181]. TFA enhances the radical cation stability and suppresses the nucle-ophilicity of water. Of further advantage is the addition of alumina or trifluo-roacetic anhydride [182]. Table 12 compiles representative examples of the aryl ether coupling. 

A peri-fused system can be synthesized by diaryl copper-catalyzed ether coupling accomplished utilizing (CuOTf)2 PhMe in pyridine (Equation (21) (2004JOC4527)). This protocol produces several annulated ring systems and gives... 

Substitution reactions at aromatic carbon (see also Reduction reactions, Ullmann ether coupling, specific reactions such as Nitration) Arene(tricarbonyl)chromium complexes, 19... 

Benzylic silyl ethers couple with allylsilanes in the presence of trityl tetrakis [3,5-bis(trifluoromethyl)phenyl]borate (TFPB) catalyst leading to carbon-carbon bond formation (equation 77). The corresponding Z11CI2-catalyzed reactions with an allyl silyl ether lead to a mixture of regioisomers145,146. 

J.-F. Marcoux etal, US Patent 6,395,939 (May 28, 2002) Assignee Massachusetts Institute of Technology Utility Aromatic Ether Coupling Reagent... 

Acylation of aryl and alkenyl halides. The zinc salts of enol ethers and allenic ethers couple with aryl and alkenyl halides in the presence of several Pd(0) catalysts Pd[P(QH,),l4 or bis(dibenzylideneacetone)palladium with added phosphine ligands. 

Returning to phenol ether-phenol ether coupling, synthetic septicine (59) gave ( )-tylophorine (60) on treatment with thallium trifluoroacetate, and the same reagent converted synthetic julandine (61) to ( )-cryptopleurine (62 69%). In another synthesis of tylophorine the lactam (63) was transformed with va-... 

Electrooxidation is also viable for phenol ether-phenol ether coupling and has been thoroughly investigated. For example a range of compounds (65) with R = H or Me, Z = CH2 or O, = 1 or 2, reacted at the anode to give fair yields of the corresponding biaryls (66), together with spirodienone products (see Section 2.9.3.2). 

Molecules that can respond to external stimuli are of particular interest for macromolecular devices, and may potentially serve as molecular switches. A number of groups have examined the incorporation of photochemically responsive cores into dendritic structures. Azobenzene moieties, which are capable of undergoing a photochemical cis—trans isomerization, were first incorporated into the core of poly(aryl ether) dendrimers (Figure 15) via a Williamson ether coupling by Aida and co-workers313-315 and shortly thereafter, by Junge and McGrath.316 UV irradiation of the samples converted the more stable trans... 

An alternative approach developed by Schluter and co-workers involves the attachment of convergently prepared dendrons onto a preformed, functional linear polymer. This was first attempted by the Williamson ether couplings between dendritic bromides and pendant hydroxyl groups on poly([ 1.1.1]-propellane)412 and polyp-phenylene).413 Nearly quan-... 

An investigation of the photochenical reactivity of the quinone (393) in crown ethers (394) (n = 1, 2. or 3) has been carried out. The products from the reaction have been identified as the adducts (395). The formation of these is thought to arise by hydrogen abstraction by the quinone from the crown ether. Coupling between the resultant radicals affords the observed... 

Pivaloyl chloride coupling agent, antifreeze PPG-3 methyl ether coupling agent, antiknock gasoline 1,1-Dichloroethane coupling agent, antiperspirant sticks PPG-10 butanediol... 

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