The enantioselective functionalization of nonactivated enantiotopic secondary CÀHbonds is one of the greatest challenges in transition-metal-catalyzed C À Ha ctivation proceeding by an inner-sphere mechanism. Suchr eactions have remained elusive within the realm of Pd 0 catalysis.R eported here is the unique reactivity profile of the IBiox ligand family in the Pd 0-catalyzed intramolecular arylation of such nonactivated secondary CÀHb onds.C hiral C 2-symmetric IBiox ligands led to high enantioselectivities for ab road range of valuable indane products containing atertiary stereocenter,as well as the arylation of secondary C À Hb onds adjacent to amides.Depending on the amide substituents and upon control of reaction time,indanes containing labile tertiary stereocenters were also obtained with high enantioselectivities.A nalysis of the steric maps of the IBiox ligands indicated that the level of enantioselectivity correlates with the difference between the two most occupied and the two less occupied space quadrants,and provided ab lueprint for the design of even more efficient ligands.
The enantioselective functionalization of nonactivated enantiotopic secondary C−H bonds is one of the greatest challenges in transition‐metal‐catalyzed C−H activation proceeding by an inner‐sphere mechanism. Such reactions have remained elusive within the realm of Pd0 catalysis. Reported here is the unique reactivity profile of the IBiox ligand family in the Pd0‐catalyzed intramolecular arylation of such nonactivated secondary C−H bonds. Chiral C2‐symmetric IBiox ligands led to high enantioselectivities for a broad range of valuable indane products containing a tertiary stereocenter, as well as the arylation of secondary C−H bonds adjacent to amides. Depending on the amide substituents and upon control of reaction time, indanes containing labile tertiary stereocenters were also obtained with high enantioselectivities. Analysis of the steric maps of the IBiox ligands indicated that the level of enantioselectivity correlates with the difference between the two most occupied and the two less occupied space quadrants, and provided a blueprint for the design of even more efficient ligands.
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Block copolymers are highly interesting materials in light of their unique ability to form organized structures via self-assembly. Developing one-step syntheses of controlled block copolymers is desirable but challenging, due to the usually low reactivity differences of the used monomers. Ring-opening metathesis polymerization (ROMP) could provide a solution to this problem, in addition to its robustness and chemoselectivity. In this work, the authors investigate the effect of monomer substituents on ROMP rates and block copolymer structures. By mixing monomers with different steric properties, copolymers with the sharpest gradient compositional profile known to date could be obtained. A retardation technique, based on the reversible formation of a Fischer carbene, allowed analysis of the fastest reacting polymers by 1 H NMR spectroscopy. This method could serve as a general tool to study fast ROMP reactions. Authors' comments:"Targeting exact block ratios in block copolymers can be a difficult task. Here, all you need to do is mix the two monomers, add a Grubbs initiator and 'Bob's your uncle'."
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