Salts of 1-(Chloromethyl)-DABCO: A Highly Efficient Organocatalyst for the Alcoholysis of Epoxides

Abstract

Background: Epoxides are useful and important intermediates in pharmaceutical and agrochemical industries. In particular, the opening of epoxides with alcohols is an important transformation for the synthesis of β-alkoxy alcohols which are considered as valuable organic solvents, versatile synthons and intermediates. We have synthesized simple, highly efficient and environment benign catalyst and applied for the ring opening of epoxides with alcohols at room temperature. Methods: All the chemicals were purchased from commercial sources. Solvents used for the chemical synthesis were acquired from commercial sources, were of analytical grade and used without further purification. Thin layer chromatography (Merck Kiesel 60 F254, 0.2 mm thickness) was used to monitor the progress of the reactions and the compounds were purified by silica gel (60-120 mesh) column chromatography. Determination of the purity of the substrate and reaction monitoring were accomplished by GC analysis (Shimadzu GC-2010 Plus) using N2 as a carrier gas and Rtx-5 column (30 m x 0.25 mm x 0.25 mm, Restek, USA). 1H NMR (400 MHz) and 13C NMR (100 MHz) spectra were recorded on Jeol ECX FT-NMR instrument using CDCl3 as solvent and TMS as internal reference. The chemical shift values were expressed on δ scale and the coupling constant (J) in Hz. Results: The quaternary salts of 1-(chloromethyl)-DABCO was synthesised from 1-(chloromethyl)-4- aza-1-azonia-bicyclo[2.2.2]octane tetrafluoroborate and different acids in acetone at 25 °C temperature. These salts were exhibits high catalytic activity for the ring opening of epoxides and gave corresponding β-alkoxy alcohols in good to excellent yields. Styrene oxide and phenyl glycidyl ether gave completely regioselective β-alkoxy alcohol. Conclusion: We have synthesized simple, convenient, highly efficient salts of 1-(chloromethyl)- DABCO and applied as organocatalysts (0.127 mol%) for the regioselective ring opening of epoxides with methanol. Ring opening of styrene oxide with different alcohols to afforded β-alkoxy alcohols in good to excellent yields. The cyclic epoxides gave trans-2-methoxy-cyclic alcohols in excellent yields. The catalyst also catalyzed the less reactive epoxide like glycidyl ethers, epichlorohydrin required a high loading of organocatalyst 3 (2 mol%) to complete the reaction. Keywords: Alcoholysis, epoxides, salt of DABCO, alkoxy ethers, ring opening of epoxides.