A New Method for Installation of Aryl and Alkenyl Groups onto a Cyclopentene Ring and Synthesis of Prostaglandins.

To construct a new strategy for synthesis of cyclopentanoids, the transition metal-catalyzed coupling reaction of cis 4-cyclopentene-1,3-diol monoacetate 1 with hard nucleophiles, RT−m, was investigated (eq 1 in Chart 1). Although preliminary experiments using PhZnCl, PhSnMe3, [Ph-B(Me)(OCH(Me)CH(Me)O)]-Li+ (6a) (derived from boronate ester 4a (RT = Ph) and MeLi) in the presence of a palladium or a nickel catalyst resulted in production of unidentified compounds, enone 16, and/or ketone 17 or recovery of 1, a new borate 5a (derived from 4a and n-BuLi) in the presence of a nickel catalyst (NiCl2(PPh3)2) in THF at room temperature furnished the trans coupling products 2a (RT = Ph) and 3a (RT = Ph) in high combined yield, but with a low product ratio of 0.9:1. The ratio was improved to 13:1 by addition of t-BuCN and NaI into the reaction mixture. This is the first successful example of the reaction of 1 with a hard nucleophile, and the increase in the ratio, realized with the additives, is unprecedented. Thi...