[reaction: see text] Cyclopropanation of allylic tertiary amines using the Simmons-Smith reagent has been achieved by employing chelating groups in close proximity to the amine. The chelating groups promote cyclopropanation at the expense of N-ylide formation. Using pseudoephedrine as the chelating group, high diastereoselectivity is observed.
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http://dx.doi.org/10.1021/ol035713b | DOI Listing |
Org Lett
December 2024
School of Chemistry, Dalian University of Technology, Dalian 116024, P. R. China.
An efficient palladium-catalyzed -allylic alkylation of pyrazoles and unactivated vinylcyclopropanes is demonstrated, affording various -alkyl pyrazoles in ≤99% yield. This protocol displays high atom economy, a broad range of substrates, and excellent regioselectivity and stereoselectivity. Late-stage modification of bioactive molecules, scaled-up reaction, and divergent derivatization documented the practicability of this methodology.
View Article and Find Full Text PDFJ Am Chem Soc
November 2024
Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, South Korea.
Transition metal carbenes have emerged as versatile intermediates for various types of alkylations. While reactions of metal carbene species with alkenes have been extensively studied, most examples focus on cyclopropanation and allylic C-H insertion. Herein, we present the first example of a catalytic strategy for the carbene-involved regioselective remote C-H alkylation of internal olefins by synergistically combining two iridium-mediated reactivities of olefin chain walking and carbenoid migratory insertion.
View Article and Find Full Text PDFJ Am Chem Soc
November 2024
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, United States.
Despite the utility of copper catalysts for the insertion of carbene moieties into C-H bonds, the copper carbene intermediate often invoked in these transformations has not been isolated. Herein, we describe the synthesis and structural characterization of a series of copper benzylidenes utilizing the sterically encumbered dipyrrin ligand (L)H. These isolated copper carbenes demonstrate intramolecular insertion into the primary C(sp)-H bond of the ligand (L)H and intermolecular insertion into ethereal and allylic C-H bonds.
View Article and Find Full Text PDFAngew Chem Int Ed Engl
December 2024
Krupp-Chair for General and Inorganic Chemistry, Saarland University, 66123, Saarbrücken, Germany.
Unlike cyclopropanes, the analogous BC species (diboriranes) tend to adopt non-classical Hückel-aromatic structures with bridging moieties R between the boron atoms. The coordination of the thus generated cyclic 2e π-system to transition metals is completely unexplored. We here report that complexation of non-classical diboriranes cyclo-μ-RBDurCPh (R=H, SnMe; Dur=2,3,5,6-tetramethylphenyl) to Fe(CO) fragments allows for the carbonylative ring expansion of the BC ring to either four- or five-membered rings depending on the nature of the BRB 3-center-2-electron bond (3c2e): The H-bridged diborirane (R=H) initially reacts with Fe(CO) to the allylic π-complex with an agostic BH/Fe interaction.
View Article and Find Full Text PDFAngew Chem Int Ed Engl
October 2024
Department of Chemistry, Department of Biochemistry and Molecular Biology, University of British Columbia, 2036 Main Mall, Vancouver, BC, Canada, V6T 1Z1.
We report a synthesis of bicyclo[2.1.1]hexanes via an intramolecular formal (3+2) cycloaddition of allylated cyclopropanes bearing a 4-nitrobenzimine substituent.
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