The first cobalt-catalyzed asymmetric Kumada cross-coupling with high enantioselectivity has been developed. The reaction affords a unique strategy for the enantioselective arylation of α-bromo esters catalyzed by a cobalt-bisoxazoline complex. A variety of chiral α-arylalkanoic esters were prepared in excellent enantioselectivity and yield (up to 97% ee and 96% yield). The arylated products were transformed into α-arylcarboxylic acids and primary alcohols without erosion of ee. The new enantioenriched α-arylpropionic esters synthesized herein are potentially useful in the development of nonsteroidal anti-inflammatory drugs. This method was conducted on gram-scale and applied to the synthesis of highly enantioenriched (S)-fenoprofen and (S)-ar-turmerone.
To show the synthetic utility of palladium/norbornene (Pd/NBE) cooperative catalysis,h ere we report concise syntheses of indenone-based natural products,p auciflorol F and acredinone A, which are enabled by direct annulation between aryl iodides and unsaturated carboxylic acid anhydrides.C ompared to the previous indenone-preparation approaches,t his method allows simple aryl iodides to be used as substrates with complete control of the regioselectivity.The total synthesis of acredinone Afeatures two different Pd/NBEcatalyzedo rtho acylation reactions for constructing pentasubstituted arene cores,i ncluding the development of an ew ortho acylation/ipso borylation. Scheme 1. Indenone/indanone containing natural products and indenone synthesis.
Herein, we describe our initial development of an asymmetric Pd-catalyzed annulation between aryl iodides and racemic epoxides for synthesis of 2,3-dihydrobenzofurans using a chiral norbornene cocatalyst. A series of enantiopure ester-, amide- and imide-substituted norbornenes have been prepared with a reliable synthetic route. Promising enantioselectivity (42–45% ee) has been observed using the isopropyl ester-substituted norbornene (N1*) and the amide-substituted norbornene (N7*).
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