Transition-metal-catalyzed allylic alkylation is one of the most powerful methods for the enantioselective synthesis of molecules bearing new carbon-carbon bonds.  However, the formation of simple allylated ester products bearing an <i>α</i>-quaternary stereogenic center still represents a major challenge for transition metal-catalyzed allylic alkylation chemistry.  This is especially true when a disubstituted ketene is used as the reactant partner for allylic electrophiles.  We have previously demonstrated that disubstituted ketenes can be converted in enantioselective fashion to a variety of four membered ring systems through phosphine or alkaloid nucleophilic catalysis.  Recently, we investigated the catalytic asymmetric synthesis of chiral esters from disubstituted ketenes and allyl aryl ethers.  We found that when a Pd(0) catalyst (2.5 mol%) and a chiral phosphepine (5 mol%) was used as the catalytic system, to promote the reaction of disubstituted ketenes with allyl aryl ethers, that chiral aryl esters bearing an <i>α</i>-quaternary stereogenic center were formed in good to excellent yields (65-92%), with excellent regioselectivity, and with moderate to good enantioselectivity (up to 83% ee).  Details of reaction optimization, substrate scope, reaction mechanism, including a rationale for regioselectivity and enantioselectivity, will be presented.

Catalytic enantioselective synthesis of chiral esters from ketenes and allyl aryl ethers

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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