Simultaneous Induction of Axial and Planar Chirality in Arene–Chromium Complexes by Molybdenum‐Catalyzed Enantioselective Ring‐Closing Metathesis

Abstract

The molybdenum-catalyzed asymmetric ring-closing metathesis of the various Cs -symmetric (π-arene)chromium substrates provides the corresponding bridged planar-chiral (π-arene)chromium complexes in excellent yields with up to >99 % ee. With a bulky and unsymmetrical substituent, such as N-indolyl or 1-naphthyl, at the 2-positions of the η(6) -1,3-diisopropenylbenzene ligands, both biaryl-based axial chirality and π-arene-based planar chirality are simultaneously induced in the products. The axial chirality is retained even after the removal of the dicarbonylchromium fragment, and the chiral biaryl/heterobiaryl compounds are obtained with complete retention of the enantiopurity.

Conversion of two stereocenters to one or two chiral axes: atroposelective synthesis of 2,3-diarylbenzoindoles

“…In 2010, Kitagawa reported Pd-catalyzed hydroaminocyclization to construct indole N -aryl axial chirality 18. Later, Kamikawa, Takahashi and Ogasawara reported an enantioselective desymmetrising ring-closing metathesis strategy to prepare axially chiral indole N -aryl compounds 19. Very recently, Shi and Tan independently reported a well-designed chiral phosphoric acid-catalyzed asymmetric synthesis of indol C(3)-aryl axial chirality;20 Gu reported Pd-catalyzed dynamic kinetic intramolecular C–H cyclization to construct indol C(3)-aryl atropisomers 21.…”

Axially Chiral Aryl‐Alkene‐Indole Framework: A Nascent Member of the Atropisomeric Family and Its Catalytic Asymmetric Construction

“…Indole‐based axially chiral skeletons have recently attracted increasing attention from chemists due to the unique properties of the indole ring and the importance of axially chiral indole‐containing scaffolds . To fulfill the above‐mentioned task, we designed alkene‐indoles as a new class of axially chiral alkene‐ heteroaryl frameworks (Scheme c).…”

“…Indolylmethanols have proven to be versatile reactants for constructing indole‐containing scaffolds . Based on our experience with indolylmethanols, [16c,17a,20] we envision that 3‐alkynyl‐ 2‐indolylmethanols as a new class of indolylmethanols can serve as building blocks for constructing alkene‐indole frameworks. In detail, the incorporation of an alkyne functionality bearing a bulky terminal R group in the structure of 2‐indolylmethanol generates the desired C=C bond when using a nucleophile to attack the alkynyl group.…”

Enantioselective syntheses of atropisomers featuring a five-membered ring

“…28 They started from functionalised prochiral planar (p-arene)chromium complexes of type 22 bearing an indolyl substituent whose orientation is fixed in the anti configuration [Cr(CO) 2 group and the benzo moiety of the indolyl substituent are on opposite sides with respect to the p-arene plane]. The reactions were run in benzene at 40 1C with 10 mol% of in situ generated chiral molybdenium catalyst 23.…”