Phenol-Containing Macrocyclic Diamides as New Catalysts in the Highly Regioselective Conversion of Epoxides to beta-Hydroxy Thiocyanates

The regioselective ring-opening reactions of some epoxides with ammonium th iocyanate in the presence of a series of new phenol-containing macrocyclic diamides and also dibenzo-18-crown-6-, 18-crown-6-, benzo-15-crown-5-, and pyridine-containing macrocyclic diamide have been studied. The epoxides wer e subject to cleavage by NH4SCN in the presence of these catalysts under mi ld reaction conditions in various aprotic solvents. In this study, reagents and conditions have been discovered with which the individual beta -hydrox y thiocyanates can be synthesized in high yield and with more than 90% regi oselectivity. The results can be discussed in terms of a four-step mechanis m: (1) formation of complex between catalyst and NH4SCN, (2) release of SCN - nucleophile from the complex, (3) reaction of the active nucleophile at t he less sterically hindered site in the epoxide, and (4) regeneration of ca talyst. The major advantages of this method are as follows: (1) high regios electivity, (2) simple regeneration of catalyst, (3) its reuse through seve ral cycles without a decrease in activity, and (4) ease of workup of the re action.