Reductive Coupling of Terpenic Allylic Halides Catalyzed by Cp₂TiCl:  A Short and Efficient Asymmetric Synthesis of Onocerane Triterpenes

Abstract

[reaction: see text] Titanocene chloride catalyzes the regioselective alpha,alpha'-homocoupling of terpenic allylic halides. This process has been employed in the short and effective synthesis of terpenoids such as beta-onoceradiene (1), beta-onocerin (2), and squalene (3). Evidence is presented for eta1-allyltitanium species being involved in the coupling.