| Popis: |
An efficient alternative to the Ullmann ether synthesis of diaryl ethers, diaryl thioethers, and diarylamines involving the S(N)Ar addition of a phenol, thiophenol, or aniline to an appropriate aryl halide, mediated by potassium-fluoride alumina and 18-crown-6 in acetonitrile or DMSO, is described. Expansion of the reaction conditions to include DMSO as solvent has resulted in a far greater range of substitution patterns permitted on the electrophile. For example, it was found that electronically unfavorable 3-chlorobenzonitrile could be condensed with 3-methoxyphenol to form the corresponding diaryl ether in 66% yield, a combination not normally amenable to Ullmann coupling. Electron-withdrawing groups present on the electrophile may be as diverse as nitro, cyano, formyl, acetyl, ester, amide, and even aryl. The method features a simple reaction procedure that provides products in generally good to excellent purified yields. |
