Potassium Fluoride on Alumina (KF/A12O3)

Abstract

(A) Sawyer et al. have demonstrated the use of KF/Al2O 3 and 18-Crown-6 to synthesize diaryl ethers, diarylthio ethers, and diaryl amines via SNAr type addition reaction of phenol, thiophenol, and aniline to 2-fluorobenzonitrile respectively. The optimization of the above reaction conditions led to the synthesis of compounds, which were unachievable using Ullman coupling. For example, electronically unfavorable 3-chloro benzonitrile can be condensed with 3-methylphenol to give corresponding diaryl ether in 66% yields using KF/Al2O3. 18-Crown-6 in DMSO at 140°C.10 (Equation Presented) (B) Glaser coupling reactions to generate diacetylenes using KF/ Al2O3 with CuCl2 and solvent free conditions under microwave irradiation have been optimized by Kabalka et al. The use of two different alkynes, however gives a mixture of products.11 (Equation Presented) (C) Silveira et al. have reported the use of KF/Al2O3 for the synthesis of 3,4-dihydroisoquinolines and isoquinolines by desulfonylation of N-sulfonyltetrahydroisoquinone derivatives. Microwave irradiation (490 W) of the solid-state reaction mixture containing the substrate and base for 10-20 s gives 3,4-dihydroisoquinoline, which on increasing the time leads to the formation of correspond-ing isoquinoline.12 (Equation Presented) (D) KF/Al2O3 selectively desilylates the tert-butyldimethylsilyl protected phenol at room temperature. Acetonitrile as the solvent eliminates the need for an aqueous work up and the use of ultrasound accelerates the reaction thereby reducing reaction times.13 (Equation Presented) (E) Selective O-demethylation of arylalkyl ethers has also been accomplished using KF/Al2O 3 and dry ethylene glycol in 3-5 h at 210-215°C in moderate to high yields.14 (Equation Presented).