PtCl_2-Catalyzed Tandem Enyne Cyclization/1,2 Ester Migration Reaction Controlled by Substituent Effects of All-Carbon 1,6-Enynyl Esters

摘要

Cyclopentenes are important structural motifs in many natural products of significant bioactivity such as Roseophilin, Scabronine G, and Przewalskin B (Figure 1). In the past two decades, numerous methods to prepare cyclopentenes based on simple acyclic building blocks have been developed. Among them, transition metal-catalyzed (especially Pt, Au, and Ru) 1,6-enyne cycloisomerization reactions play an extremely important role considering their atom-economy and synthetic efficiency. Propargylic esters, which are well known for their transition metal-catalyzed 1,2- and 1,3-acyloxy migrations reactions, are a specific class of alkynes that have been studied by many groups. Among them, the 1,n-enyne esters are most widely used. However, in most studies, an acetate group was required to be located between the alkyne and the alkene group. Recently, several groups reported examples of 1,n-enyne esters in which an acyloxy group was located on the far side of the triple bond away from the alkene. In all cases, however, no enyne cycloisomerization products were obtained.