W(OTf)(6)-Catalyzed Synthesis of gamma-Lactones by Ring Contraction of Macrolides or Ring Closing of Terminal Hydroxyfatty Acids in Ionic Liquid

摘要

gamma-Lactones are an important class of fine chemical products and are widely used in perfumes, medicines, pesticides, dyes, and other fields. Herein, a new method for gamma-lactones preparation based on ring contraction was developed. Starting from macrolides, W(OTf)(6) was used to catalyze the ring-opening polymerization then depolymerization. The depolymerization step was not a common ring-closing process, and the carbon number of the ring was reduced one by one by rearrangement to form the most thermodynamically stable five-membered ring compounds. gamma-Caprolactone (180 degrees C for 10 h) was obtained in a yield of 94% when [EMIM]OTf was used as the solvent, and the yield of isolated product was up to 85%. The interaction of various components and the reaction mechanism were studied by FTIR spectroscopy and (HNMR)-H-1 spectroscopy, respectively. Furthermore, gamma-lactones could be produced when the substrate was extended to terminal hydroxyfatty acids. Unexpectedly, the catalyst was poisoned by 1 equivalent of H2O added during the process and thus the yield decreased greatly. The reaction is green and simple, and proceeds in one pot with high atom economy (100% for macrolides and with water as the only byproduct for terminal hydroxyfatty acid), which provides a promising approach to synthesizing gamma-lactones.