ニッケル触媒を用いる１，３‐ジエンとカルボニル基との立体選択的環化反応の開発と有機合成への応用

Abstract

A nickel-promoted intramolecular cyclization of 1, 3-diene with the tethered carbonyl group was developed using the catalyst generated by reduction of Ni(acac)2 with DIBAL-H in the presence of PPh3. The reaction course of this cyclization can be accounted for by two possible mechanisms. In one mechanism, a nickel hydride complex plays a key role and the cyclization proceeds via πallylnickel intermediate. In the other mechanism, a zerovalent nickel complex is the active species and the cyclization proceeds via the nickelacycle intermediate. These mechanistic considerations led to find two nickel (0) -catalyzed cyclizations of 1, 3-diene and the tethered aldehyde, in which the five- to seven-membered ring products were produced in a regio- and stereoselective manner via, π-allylnickel intermediate (Type I cyclization) or via transmetalation process of nickelacycle intermediate with iBu2Al-acac (Type II cyclization). We also succeeded in applying these cyclizations to the syntheses of (-) -elaeokanine C and (+)-prostaglandin F2α, and in demonstrating the catalytic asymmetric cyclization using Type I cyclization.