Synthesis and Design of Stereogenic-at-Metal Complexes and their Applications in Asymmetric Catalysis
Part 1: Post Complexation Cross-Coupling Reactions A straight forward method for post-complexation derivatizations of diastereomerically pure bis-cyclometalated benzoxazole and benzothiazole iridium(III) complexes was developed. Triflate- and bromide-functionalized iridium(III) complex dimers (sev...
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|Summary:||Part 1: Post Complexation Cross-Coupling Reactions
A straight forward method for post-complexation derivatizations of diastereomerically pure bis-cyclometalated benzoxazole and benzothiazole iridium(III) complexes was developed.
Triflate- and bromide-functionalized iridium(III) complex dimers (seven examples, up to 89% yield), were converted to the corresponding diastereomeric complexes (eleven examples up to 40% yield for each diastereomer), using readily available chiral salicyloxazolines and salicylthiazolines as ancillary ligands. The diastereomer complexes, formed as mixtures of diastereomers, were then resolved by flash chromatography and the diastereomerically pure complexes subjected to SUZUKI cross-coupling reactions (18 examples up to 94% yield). Using CD spectroscopy and HPLC analysis it was evaluated that the post-complexation cross-coupling reactions proceed without affecting the metal-located stereocenter and hence provide post-complexation derivatized non-racemic iridium(III) complexes, which were not easily accessible with previous methods.
This strategy expands the toolbox to access functionalized non-racemic iridium(III) complexes for diverse applications in life sciences, materials sciences, and catalysis i.e.: “Synthesis of a stereogenic-at-metal catalyst immobilized on solid support.”
Part 2: Asymmetric Nazarov Cyclization Reactions
The application of LEWIS acidic stereogenic‐at‐metal complexes of iridium(III) and rhodium(III) as catalysts for the asymmetric polarized NAZAROV cyclization of 3,4-dihydropyran‐ and indole‐functionalized α‐unsaturated β‐ketoesters was developed (overall 24 examples). For both substrate classes, catalyst loadings of 2.0 mol% were found to be sufficient for achieving high yields and high stereoselectivities. The cyclized 3,4-dihydropyran products were isolated in 85→98% yield, with 89%→99% ee, and trans/cis ratios of 15:1→50:1 (nine examples). The cyclized indole products were isolated in more than 70% yield, up to 97% ee, and trans/cis ratios of 12:1→28:1 (15 examples). In case of the indole substrates, a strong solvent dependence on hexafluoro-iso-propanol was observed.|
|Physical Description:||352 Pages|