A new C 2 -symmetrical, chiral bisphosphorus ligand proved to be efficient for the rhodiumcatalyzed nucleophilic addition of arylboronic acids to trifluoromethyl ketones, providing a series of chiral trifluoromethyl-substituted tertiary alcohols in high yields (up to 93%) and excellent enantioselectivities (> 99%).
Pd/CPhos-catalysis provides direct arylation/cyclisation of methylene-linked bis-anilines to dibenzo[1,3]diazepines v, which are both non-(C2)-symmetrical and axially chiral. Synthesis of the direct arylation substrates commences with substitution of (N-acyl)anilines to methylene methyl sulfide derivatives, followed by halogenation/de-thiomethylation to N-(chloromethyl)anilines. These are substituted with a second aniline derivative, allowing modular preparation of (ortho-halo)aryl-aminal-linked arenes 4. The C–H functionalising direct arylation conditions were adapted from Fagnou and co-workers: substrates and potassium carbonate were heated in dimethylacetamide in the presence of palladium acetate and an electron-rich and sterically hindered biarylphosphine ligand, here CPhos 5. These conditions delivered the C1-(a)symmetric dibenzo[1,3]diazepine targets, which, due to torsion around the axis of the newly formed biaryl bond, are also intrinsically atropisomeric. The axially twisted scaffold is known to impart special properties to ligands/catalysts when the products are further converted into the corresponding seven-membered ring-containing N-heterocyclic carbenes (e.g. xii and xiv).
The synergy of biocatalysis and transition metal catalysis is rapidly moving forward, providing increasingly effective workflows in chemical synthesis. Here we present a facile way to prepare synthetically challenging O‐containing heterocycles bearing disubstituted stereogenic centers via catalytic chemoenzymatic transformation of α‐diazo carbonyl compounds. We demonstrate that keto‐α‐diazoesters can be enzymatically reduced to the corresponding alcohols with exquisite enantioselectivity and under retention of the diazo group using the ketoreductases LbADH and Gre2p. To further functionalize the resulting enantiopure (R)‐ and (S)‐hydroxyl α‐diazo esters, a variety of Cu and Rh catalysts were screened for intramolecular ring closure. Six‐ and seven‐membered rings with both, aliphatic and ester substituents, were obtained with up to 93 : 7 diastereomeric ratio and 81 % yield. Up to 98 % enantiomeric excess was obtained for both diastereomers, yielding the thermodynamically less favored α,ω‐trans‐oxepanes as the main products.
New catalysts for important C–N bond formation are highly sought after. In this work, we demonstrate the synthesis and viability of a new class of planar chiral [2.2]paracyclophane-based bisoxazoline (BOX) ligands for the copper-catalyzed N–H insertion of α-diazocarbonyls into anilines. The reaction features a wide substrate scope and moderate to excellent yields, and delivers the valuable products at ambient conditions.
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