Abstract Highly functionalized cyclopropanecarboxylates were readily prepared by rhodium-catalyzed cyclopropanation of alkenes with aryldiazoacetates and styryldiazoaceates, in which the ester functionality is either trimethylsilylethyl (TMSE) or trichloroethyl (TCE). By having labile protecting groups on the ester, chiral triarylcyclopropane carboxylate ligands were conveniently prepared. The asymmetric induction during cyclopropanation is dependent on the nature of the ester group and the chiral dirhodium tetracarboxylate catalyst. The prolinate catalyst Rh2(S-DOSP)4 was the optimum catalyst for asymmetric intermolecular cyclopropanation of TMSE diazoesters with styrene, while Rh2(R-BPCP)4 was the optimum catalyst for TCE diazoesters.
Bibliographical noteFunding Information:
Changming Qin is acknowledged for preliminary data on the synthesis of 8 from the methyl ester 7 and the observation that the hydrolysis of the methyl ester in 7 results in racemization of the product. This work was supported by the National Science Foundation under the CCI Center for Selective C–H Functionalization , CHE-1205646 , the National Institutes of Health ( GM099142 ) and unrestricted support from Novartis.
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- Asymmetric cyclopropanation
- Dirhodium catalysis
- Donor/acceptor carbenoids