Organocatalytic Enantioselective Functionalization of Unactivated Indole C(sp 3 )−H Bonds

Iron-Catalyzed Friedel-Crafts-type 3,5-Diacylation of Indoles

The exploration of remote functionalization of indoles is impeded by the inherently dominant reactivity intrinsic to the pyrrole moiety. Herein, we delineate a novel strategy facilitated by Lewis acid mediation, enabling the remote C-H functionalization, which culminates in the synthesis of an array of selectively functionalized indole derivatives, encompassing 3-trifluoroacetyl and 5-benzoyl motifs, utilizing trifluoroacetic anhydride and various acyl chlorides. Notably, the protocol exhibits versatility, as epitomized by the extension of C5-acylation to alkylation and sulfonation reactions. This methodology is distinguished by its exemplary regio- and chemo-selectivity, extensive substrate scope, commendable tolerance to a diverse array of functional groups, and the employment of comparatively mild reaction conditions.

Metal-Free C(sp3)-H Bond Arylation of 3-Methylindole Derivatives via 3-Indole Imine Methides

Direct arylation of the benzylic C(sp3)-H bond is one of the most straightforward strategies for the construction of multi-aryl methanes, owing to the extraordinary step and atom economy. In this paper, we developed the first metal-free arylation of the C(sp3)-H bond in 3-methylindoles, thereby providing rapid access to a range of diaryl- and triarylmethanes with two indole rings. Mechanistically, 3-indole imine methide serves as the key intermediate. Water plays a crucial role in this process, likely serving as a proton shuttle to facilitate the key 1,3-proton transfer step in this reaction and, thus, enhance the reaction efficiency.

Stereoselective Synthesis of Atropisomeric Acridinium Salts by the Catalyst‐Controlled Cyclization of ortho ‐Quinone Methide Iminiums

Quinone methides are fundamental intermediates for a wide range of reactions in which catalyst stereocontrol is often achieved by hydrogen bonding. Herein, we describe the feasibility of an intramolecular Friedel–Crafts 6π electrocyclization through ortho‐quinone methide iminiums stereocontrolled by a contact ion pair. A disulfonimide catalyst activates racemic trichloroacetimidate substrates and imparts stereocontrol in the cyclization step, providing a new avenue for selective ortho‐quinone methide iminium functionalization. A highly stereospecific oxidation readily transforms the enantioenriched acridanes into rotationally restricted acridiniums. Upon ion exchange, the method selectively affords atropisomeric acridinium tetrafluoroborate salts in high yields and an enantioenrichment of up to 93 : 7 e.r. We envision that ion‐pairing catalysis over ortho‐quinone methide iminiums enables the selective synthesis of a diversity of heterocycles and aniline derivatives with distinct stereogenic units.

Carbene-Catalyzed Activation of Formyl-phenylacetic Esters for Access to Chiral Dihydroisoquinolinones

A carbene-catalyzed reaction to synthesize chiral dihydroisoquinolinones via an o-quinodimethane (o-QDM) intermediate is disclosed. o-QDM reacts with cyclic sulfonic imines via annulation to afford highly enantioenriched dihydroisoquinolinone products. ESI-HRMS studies suggest a stepwise Mannich addition and acylation reaction pathway, and the pathways of the catalytic and uncatalyzed background reactions are evaluated via DFT calculations.

Organocatalytic asymmetric allylic alkylation of 2-methyl-3-nitroindoles: a route to direct enantioselective functionalization of indole C(sp3)-H bonds

We here described a direct catalytic asymmetric functionalization of 2-methylindoles using organocatalysis. An efficient asymmetric allylic alkylation reaction with respect to 2-methyl-3-nitroindoles and racemic Morita-Baylis-Hillman carbonate has been achieved by using a chiral biscinchona alkaloid catalyst, which provided the functionalized indole derivatives in good yields and enantioselectivities.

Regioselective C5-H direct iodination of indoles

An efficient regioselective C5-H direct iodination of indoles is reported herein for the first time, which offers a general and practical access to the difficult C5 functionalization of indoles.

Fe-Catalyzed Sequential C(sp3)-H/N-H Annulation of 2-Methylindoles with Ethyl Trifluoropyruvate at Room Temperature: Construction of Pyrrolo[1,2-α]indoles

An efficient and benign iron-catalyzed room-temperature method was developed for direct sequential C(sp³)-H/N-H annulation to construct pyrroloindole scaffolds. This strategy features cheap and readily available raw materials and mild room-temperature reaction conditions and provides a green and practical method for the one-pot rapid synthesis of a wide range of diversely functionalized pyrrolo[1,2-α]indoles.