Efficient transformation of lower esters to functionalized compounds are highly desirable since they are abundant, commercially available and inexpensive. Herein, we report transesterification reaction promoted by the developed zinc catalysts (Scheme 1) and intermolecular [3+2] cycloaddition reaction of donor-acceptor (D-A) cyclopropanes and sulfur containing dipolarophiles derived from lower esters (Scheme 2). Catalytic transesterification is one of the most ideal ester synthesis method because of its broader functional group compatibility and higher atom-economy in comparison with traditionally performed strong acid or condensation reagent mediated method. However, reported metal catalysts have several problems such as high toxicity, cost or low catalytic activity. Recently, we succeeded in the development of highly stable but active zinc/ligand complex 2, allowing for performing the transesterification without strict concern regarding air and moisture with wide substrate generalities. Moreover, we also developed universal and recyclable heterogeneous catalyst 3 with broad spectrum of reactions and solvents. The recovered catalyst 3 was reused at least four times without loss of the catalytic activity. Intermolecular cycloaddition reaction using hetero atom containing dipolarophiles is a highly powerful tool for the synthesis of functionalized heterocycles. Although sulfur containing heterocyclic scaffolds have been seen in various biologically active compounds, catalytic methodology for cycloaddition of sulfur containing dipolarophiles are quite limited because of their highly unstable and strong soft Lewis basic characteristics. Recently, we succeeded in the development of iron(III) triflate catalyzed [3+2] cycloaddition of D-A cyclopropanes and thionoesters as a synthetic route to α-alkoxy tetrahydrothiophenes (THTs). Not only aromatic and aliphatic thionoesters, but also thionolactone were applicable to the catalysis. Further transformation of S,O-ketal functionality of the cycloadduct was achieved in a highly diastereoselective manner affording trans-configured THTs.

Efficient use of lower ester compounds: Catalytic transesterification and cycloaddition

256th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.