Metal-free cascade boron–heteroatom addition and alkylation with diazo compounds

Gold/silver-catalyzed synthesis of functionalized indoles from N-allyl-2-alkynylanilines and α-diazo compounds via 1,3-allyl migration

Gold-catalyzed synthesis of decorated indoles has been developed through carbene insertion into N-H bonds of N-allyl-2-(aryl/alkyl ethynyl)anilines using α-diazo compounds followed by cyclization and concomitant 1,3 migration of allyl fragments. The developed protocol tackles the inherited challenge of direct C3 functionalization and eliminates the need for a tertiary aniline precursor for the 1,3-migration reaction. The applicability of this transformation is showcased through the practical synthesis of analogs of small drug-like and pharmaceutically relevant molecules such as ibuprofen, estradiol, menthol, and borneol, etc. The mechanism is well supported by control experiments and isolation of the reaction intermediate.

Copper-Catalyzed Cascade Cyclization of 2-Nitrochalcones with NH-Heterocycles

We developed a method for allowing cascade cyclization of 2-nitrochalcones with pyrazoles, imidazole, and indazole in the presence of CuI catalyst, DBU base, and THF solvent. The conditions were tolerant of an array of useful functionalities including ester, nitro, cyano, halogen groups. A mechanistic consideration was also provided, as H2O2 was presumably a byproduct. Our method appears to be a rare example to directly prepare C3-heterocyclic unprotected indoles.

Metal-free Borylation of α-Naphthamides and Phenylacetic Acid Drug

Site-selective C-H borylation is an important strategy for constructing molecular diversity in arenes and heteroarenes. Although transition-metal-catalyzed borylation is well explored, developing metal-free strategies remains scarce. Herein, we developed a straightforward approach for BBr3-mediated selective C-H borylation of naphthamide and phenyl acetamide derivatives under metal-free conditions. This methodology appears to be economical and cost-effective. Successful borylation of drug molecules such as ibuprofen and indoprofen demonstrates the versatility and utility of this metal-free borylation. An exclusive monoselectivity was observed without a trace of diboration. Despite the possibility of forming a 5-membered boronated intermediate at the ortho-position, the selectively 6-membered intermediate paved the way for the formation of the peri-product, which was further supported by detailed computational investigation.

Catalyst-Controlled C-H Transformation of Pyrazolidinones with 1,3-Diynes for Highly Selective Synthesis of Functionalized Bisindoles and Indoles

An efficacious synthetic solution to offer functionalized bisindoles and indoles has been developed based on catalyst-controlled C-H functionalization of pyrazolidinones and 1,3-diynes with highly selective control of both chemoselectivity and regioselectivity. This straightforward pathway conquers chemo- and regioselectivity challenges concerning the use of 1,3-diynes.

Cu(OTf)2-catalyzed C3 aza-Friedel-Crafts alkylation of indoles with N,O-acetals

An efficient approach to access functionalized indole derivatives has been developed through Cu(OTf)₂-catalyzed C3 aza-Friedel-Crafts alkylation of substituted indoles 5a-5m, N-methyl-pyrrole with linear N,O-acetals 4a-4l. As a result, a series of C3 amide aza-alkylated indole derivatives 6a-6ag and 7 were synthesized in moderate to excellent yields.

Reductive cross-coupling to access C–N bonds from aryl halides and diazoesters under dual nickel/photoredox-catalyzed conditions

A reductive cross-coupling reaction to access C–N bonds via dual Ni/photoredox-catalyzed systems has been reported. This method tolerates a broad scope of functional groups and the products can be transformed into several heterocycles.