Abstract
Development of catalytic generation of allyl–metal complexes through allylic C–H cleavage of alkenes without prefunctionalization followed by site- and stereoselective carbon–carbon bond formation is of great importance in organic synthesis, providing a straightforward and step-economical approach to introduce a versatile allyl group into organic molecules. Although significant advances have been achieved in enantioselective transformations of electrophilic allyl–metal complexes and allyl radicals, enantioselective reactions of nucleophilic allyl–metal intermediates furnished through allylic C–H cleavage remain undeveloped. Herein, we identify a multi-tasking chiral catalyst derived from a commercially available phosphine ligand and cobalt salt that precisely controls the chemoselective formation of the allyl–cobalt complex and the site- and stereoselective addition to carbonyls, delivering a broad scope of homoallylic alcohols with high yield and stereoselectivity. This work may establish a platform for the development of enantioselective transformations of nucleophilic organometallic complexes generated from catalytic C–H functionalization.
Highlights
Transition-metal-catalyzed carbon–hydrogen (C–H) bond functionalization has long been central to researchers in organic chemistry, as it enables direct installation of functional groups without the need of multistep manipulations to introduce functionalities, allowing significant shortening synthetic routes and improving the overall efficiency of organic synthesis.[1,2,3,4,5] activation of C(sp2)–H bonds promoted by transition-metal complexes have been well-studied, catalytic functionalization of C(sp3)–H bonds has been much less developed due to their inherent inertness to metal complexes insertion and low reactivity and instability of the resulting C(sp3)–metal bonds.[6,7] The greatest challenge for such process is the control of selectivity.[8]
We report a catalytic process that chemoselective formation of nucleophilic allyl–cobalt complexes through oxidative allylic C–H cleavage of alkenes followed by site, diastereo- and enantioselective addition to aldehydes and α-ketoesters
Activation of C(sp2)–H bonds promoted by transition-metal complexes have been well-studied, catalytic functionalization of C(sp3)–H bonds has been much less developed due to their inherent inertness to metal complexes insertion and low reactivity and instability of the resulting C(sp3)–metal bonds.[6,7]
Summary
Transition-metal-catalyzed carbon–hydrogen (C–H) bond functionalization has long been central to researchers in organic chemistry, as it enables direct installation of functional groups without the need of multistep manipulations to introduce functionalities, allowing significant shortening synthetic routes and improving the overall efficiency of organic synthesis.[1,2,3,4,5] activation of C(sp2)–H bonds promoted by transition-metal complexes have been well-studied, catalytic functionalization of C(sp3)–H bonds has been much less developed due to their inherent inertness to metal complexes insertion and low reactivity and instability of the resulting C(sp3)–metal bonds.[6,7] The greatest challenge for such process is the control of selectivity.[8]. We report a catalytic process that chemoselective formation of nucleophilic allyl–cobalt complexes through oxidative allylic C–H cleavage of alkenes followed by site-, diastereo- and enantioselective addition to aldehydes and α-ketoesters.
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