Pt-Catalyzed Tandem 1,2-Acyloxy Migration/Intramolecular [3 + 2] Cycloaddition of Enynyl Esters

摘要

In recent years, utilization of Pt and Au catalysts to promote reactions of enyne derivatives has attracted considerable attention in modern catalysis. Among these reports, the propargylic carboxylate is a unique class of substrates because of its significant reactivity pattern involving C≡C triple-bond activation and O-ester rearrangement. As shown in Scheme 1, the O-ester group undergoes an internal 1,3-shift catalyzed by the transition metal, giving the rearranged allenic intermediate D,4 wherein the computational calculation suggests that 1,3-acyloxy migration might also account for the double 1,2-acyloxy migrations involving the in situ generation of synthetically valuable 1,3-dipole intermediate C. To explore the diversity of reactivity of enyne chemistry, we envisioned that the intermediate C, a metal-involved 1,3-dipolar synthon, might experience cycloaddition with an appropriate olefin to generate cycloaddition product E. To our knowledge, this tandem transformation involving 1,2-acyloxy migration of propargylic carboxylates followed by 1,3-dipolar cycloaddition has not been reported previously. Herein, we present a cascade process involving PtCh-catalyzed 1,2-acyloxy migration of propargylic esters and subsequent intramolecular [3 + 2] cycloaddition, giving access to various functionalized cyclic compounds that are synthetically interesting building blocks in the total synthesis of structurally relevant natural products.