Selective Monotetrahydropyranylation of Symmetrical Diols Catalyzed by Ion-Exchange Resins

Primary and secondary symmetrical diols with 2−10 carbon atoms gave selectively monotetrahydropyranyl ethers in the reaction catalyzed by wet sulfonic acid-type ion-exchange resins in 3,4-dihydro-2H-pyran (DHP)/toluene or DHP/hexane. The yields of the monoethers were higher than 80% while those of the corresponding diethers were lower than 5%. In these reactions the rate of the formation of the diethers did not increase much even after most of the diols had been consumed. In the reaction of 1,10-decanediol in DHP/hexane, the yields of the monoether were increased by the addition of DMF or DMSO. Each diol was found to have a particular DHP/hydrocarbon ratio that gave the highest selectivity for the monoether. Generally, the larger the number of carbon atoms of the diols, the smaller the ratio of DHP in the solvents to give high selectivity for the monoether. This method of the selective etherification is quite simple and practical.