Aryl ether synthesis

Chromium activation allows a strategy for aryl ether synthesis in four stages (i) electrophilic chlorination (ii) chromium coordination (iii) alkoxide substitution for chloride and (iv) oxidative decomplexa-tion.33 The process is effective for the synthesis of 6-methoxytetrahydroquinolines and 5-methoxydihydroindole derivatives, for example. Chlorination of iV-acetyltetrahydroquinoline with SO2CI2 followed by deacetylation provides 6-chlorotetrahydroisoquinoline in 77% yield (equation 11).33 Complexation with [Cr(CO)6] in diglyme-cyclohexane at 125 °C for 53 h using the Strohmeier apparatus gave the chromium complex (13) in 85% yield, based on 40% recovery of starting material. The unre-... 

D Angelo ND, Peterson JJ, Booker SK et al (2006) Effect of microwave heating on Ullmann-type heterocycle-aryl ether synthesis using chloro-heterocycles. Tetrahedron Lett 47 5045-5048... 

The SjvAr reaction is another attractive method for diaryl ether synthesis, and reactions of o-nitro- and o-cyanofluorobenzenes with phenols were reported . 7r-Complexation of aryl halides with transition metals activates the aromatic nuclei toward S fAr. Segal employed a ruthenium chlorobenzene complex in the poly(aryl ether) synthesis , and the methodology was extensively studied by Pearson, Rich and their coworkers using manganese complex and later iron and ruthenium complexes in natural product synthesis " . The intramolecular substitution of an aromatic chloride with a phenylalanine derivative takes place at room temperature without racemization (equation 27). 

The prevalence of the aniline functional group in alkaloid natural products of medicinal interest has inspired a number of metal-catalyzed strategies for the preparation of substituted anilines. One classical method, a variation of the Ullman aryl ether synthesis, features copper catalysis. This method generally suffers from harsh reaction conditions and limited substrate scope. Nonetheless, the simplicity of the transformation and the inexpensiveness of copper catalysis has prompted additional development of this strategy. For instance, cyclohexylphenylamine is formed in excellent yield from the copper(I) iodide-catalyzed amination of iodobenzene. ... 

J.W. Labadie, J.L. Hedrick, Perfluoroalkylene-activated poly(aryl ether) synthesis. Macromolecules 23 (26) (1990)5371-5373. 

Nucleophilic displacement of an activated dihalo or dinitro compound with an activated bisphenoxide salt at high temperatures has been the most explored method of poly (aryl ether) synthesis [62], These synthetic strategies were further extended for the preparation of hb poly(aryl ether)s in one-step polymerization from AB2 monomers containing a phenolic group and two aryl fluorides, which were activated toward nucleophilic displacement by a sulfone, ketone, imide, or heterocycle [63-65]. Miller et al. [63], Hawker and Chu [65], and Shu and Leu [66] reported the synthesis of hb poly(aryl ether ket(Mie)s (hb-PAEKs) via the AB method. The structures of AB2 monomers reported by Hawker and Chu [65] are shown in Scheme 4 (1-5 and 1-6). The structiu es of AB2 monomers reported by Shu and Leu [66] are shown in 1-7, Scheme 4. 

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