Palladium-Catalyzed Asymmetric Allylic Alkylation of Cyclic Dienol Carbonates: Efficient Route to Enantioenriched γ-Butenolides Bearing an All-Carbon α-Quaternary Stereogenic Center

摘要

Since its introduction almost simultaneously by Tsuji et al. and Saegusa et al. in the beginning of the 1980s, the palladium-catalyzed decarboxylative allylic alkylation reaction has been the focus of intensive efforts and has become one of the most valuable methods for the construction of C—C bonds. Interestingly however, despite all the developments made during the next two decades, it was only in 2004 that Stoltz et al. , and Burger and Tunge reported the first asymmetric versions of this class of reaction by applying it to cyclic allyl enol carbonates and 1,3-disubstituted allylic (3-ketoesters, respectively. Immediately after, Trost et al. reported the use of a new family of ligands derived from 2-diphenylphosphinobenzoic or 1-naphthoic acid and a chiral scalemic diamine enabling the asymmetric synthesis of both cyclic and acyclic ketones bearing either a tertiary or a quaternary α-stereogenic center. Since then, this reaction has been successfully applied to a wide variety of substrates including α-sulfonyl, α-nitro, α-cyano,α-imino, orα-heteroaromatic allyl esters as well as various enol carbonates and silyl enol ethers,' thus illustrating its broad functional-group tolerance.