Abstract
Enantioselective quaternary carbon construction in the assembly of cyclopentenones employing a RhII-catalyzed, formal [4+1]-cycloaddition is described. A Rh2(S-TCPTTL)4-catalyzed cyclopropanation of a vinyl ketene with a disubstituted diazo compound initiates a stereoretentive, accelerated ring expansion to provide the cycloadduct in good to excellent yields and enantioselectivity.
Highlights
While the evolution of new enantioselective [4+1]cycloadditions has advanced considerably in recent years,[1] enabling the stereoselective polyfunctionalization of a disubstituted C1 subunit to yield quaternary stereogenic carbons remains a signi cant challenge
While diastereoselective strategies are known,11a,11c,12 few asymmetric approaches to assemble this quaternary center exist.1b,13 we describe the rst enantioselective, formal [4+1]cycloaddition between a diazo compound 1 and the vinyl ketene generated in situ from cyclobutenone 2 to provide
Attempts to isolate the cyclopropyl ketene intermediate led to the serendipitous discovery that conversion to the cyclopentenone was accelerated upon exposure to silica gel.8a,24 introduction of SiO2 following cyclopropanation yielded cycloadduct 3a in 90% yield and 90% ee.[25]
Summary
An unusual stereoretentive 1,3-quaternary carbon shift resulting in an enantioselective RhII-catalyzed formal [4+1]-cycloaddition between diazo compounds and vinyl ketenes†. Enantioselective quaternary carbon construction in the assembly of cyclopentenones employing a RhII-catalyzed, formal [4+1]-cycloaddition is described. A Rh2(S-TCPTTL)4-catalyzed cyclopropanation of a vinyl ketene with a disubstituted diazo compound initiates a stereoretentive, accelerated ring expansion to provide the cycloadduct in good to excellent yields and enantioselectivity
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