Tandem Allylboration—Ring Closing Metathesis Reactions for the Preparation of Biologically Active Molecules

The development of asymmetric synthesis during the past two decades aided or- ganic chemists considerably in the synthesis of complex natural products. Organoborane chemistry continues to play an important role in asymmetric synthesis. One of the important reactions that has become very common in the arsenal of synthetic chemists is allylboration and related reactions. Another important reaction that has recently attained enormous impor- tance in organic chemistry is the ring-closing metathesis (RCM) reaction. Indeed, a combi- nation of allylboration and RCM reactions provides an excellent route to cyclic ethers, lac- tones, lactams, etc. Herein, we describe a sequential asymmetric allylboration and RCM reaction protocol that has been utilized for the synthesis of several α-pyrone-containing nat- ural products, particularly biologically active molecules.