Chiral, substituted cyclobutanes are common motifs in bioactive compounds and intermediates in organic synthesis but few asymmetric routes for their synthesis are known. Herein we report the Rh-catalyzed asymmetric hydrometallation of a range of -cyclobutenes with salicylaldehydes. The -phenolic group promotes hydroacylation and can be used as a handle for subsequent transformations.
View Article and Find Full Text PDFSingle enantiomer molecules are important for the pharmaceutical and agrochemical industries and increasingly so in materials science. Most strategies to obtain enantiomerically enriched molecules rely on either generating new stereogenic centres from prochiral substrates or resolving racemic mixtures of enantiomers. Dynamic asymmetric processes are powerful methods that use racemic mixtures of chiral substrates as starting material.
View Article and Find Full Text PDFUsing asymmetric catalysis to simultaneously form carbon-carbon bonds and generate single isomer products is strategically important. Suzuki-Miyaura cross-coupling is widely used in the academic and industrial sectors to synthesize drugs, agrochemicals and biologically active and advanced materials. However, widely applicable enantioselective Suzuki-Miyaura variations to provide 3D molecules remain elusive.
View Article and Find Full Text PDFMechanistic studies on Cu-catalyzed asymmetric additions of alkylzirconocene nucleophiles to racemic allylic halide electrophiles were conducted using a combination of isotopic labeling, NMR spectroscopy, kinetic modeling, structure-activity relationships, and new reaction development. Kinetic and dynamic NMR spectroscopic studies provided insight into the oligomeric Cu-ligand complexes, which evolve during the course of the reaction to become faster and more highly enantioselective. The Cu-counterions play a role in both selecting different pathways and in racemizing the starting material via formation of an allyl iodide intermediate.
View Article and Find Full Text PDFCsp(2)-Csp(2) cross-coupling reactions between arylboronic acid and aryl halides are widely used in both academia and industry and are strategically important in the development of new agrochemicals and pharmaceuticals. Csp(2)-Csp(3) cross-coupling reactions have been developed, but enantioselective variations are rare and simply retaining the stereochemistry is a problem. Here we report a highly enantioselective Csp(2)-Csp(3) bond-forming method that couples arylboronic acids to racemic allyl chlorides.
View Article and Find Full Text PDFAlkenylzirconium nucleophiles made in situ by the hydrozirconation of terminal alkynes undergo dynamic kinetic asymmetric allylic alkenylation with racemic allyl bromides to give enantioenriched products.
View Article and Find Full Text PDFThe development of new reactions forming asymmetric carbon-carbon bonds has enabled chemists to synthesize a broad range of important carbon-containing molecules, including pharmaceutical agents, fragrances and polymers. Most strategies to obtain enantiomerically enriched molecules rely on either generating new stereogenic centres from prochiral substrates or resolving racemic mixtures of enantiomers. An alternative strategy--dynamic kinetic asymmetric transformation--involves the transformation of a racemic starting material into a single enantiomer product, with greater than 50 per cent maximum yield.
View Article and Find Full Text PDFThis protocol describes the catalytic asymmetric formation of all-carbon quaternary centers--a distinctive feature of many natural products and pharmaceuticals--via conjugate addition of alkylzirconium reagents to a tertiary enone. This methodology uses alkenes as starting materials and enables the incorporation of functional groups. The alkylzirconium reagent is generated in situ by mixing the alkene with the Schwartz reagent.
View Article and Find Full Text PDFThe C-Si bonds of triisopropylsilyl-substituted alkenes, 1,3-dienes, and related multifunctional substrates, as well as analogous C-TBDPS and C-TBS bonds, are readily and chemoselectively cleaved with NIS (or other sources of I(+), such as N-iodosaccharin, 1,3-diodohydantoin, and Ipy(2)BF(4)). The desired iodoalkenes are obtained stereospecifically without byproducts, provided that the reactions are carried out in CF(3)CHOHCF(3) and, in general, with 30 mol % of Ag(2)CO(3) (or AgOAc/2,6-lutidine) as an additive. Fragment C10-C18 of cytotoxic amphidinolides B1-B3 and D has been synthesized using this improved procedure.
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