Catalytic Z-Selective Cross-Metathesis with Secondary Silyl- and Benzyl-Protected Allylic Ethers: Mechanistic Aspects and Applications to Natural Product Synthesis

摘要

Allylic alcohols and derivatives are used regularly in stereoselective transformations, where the derived E and Z alkenes typically deliver different diastereomers and one geometric form reacts with higher stereoselectivity. Some recently developed Cu-catalyzed enantioselective allylic substitutions require Z-allylic phosphates or halides, entities typically prepared via the corresponding alcohols (Scheme 1). Another example pertains to diastereoselective Ti-mediated crosscoupling of allylic alcohols with imines or aldehydes. Biologically active molecules can contain Z-allylic alcohols as well; anti-cancer and immunosuppressive agent falcarindiol (1, Scheme 1) and related derivatives (e.g., 2) contain a Zalkene and neighboring alkyne units. Development of efficient catalytic methods for Z-selective synthesis of allylic ethers/alcohols is therefore a compelling objective.