Efficient copper-catalyzed synthesis of C3-alkylated indoles from indoles and alcohols

One-pot acid-catalysed synthesis of bis(1-imidazo[1,5-a]pyridyl)arylmethanes and evaluation of cytotoxic activities

A practical and efficient approach for the acid-catalysed synthesis of bis(1-imidazo[1,5-a]pyridyl)arylmethane (BimPy) derivatives has been described. Interestingly, these BimPys showed potential cytotoxicity against various cancer cell lines (SK-LU-1, MCF-7, HepG2).

Copper-catalyzed C(sp3)-H alkylation of fluorene with primary and secondary alcohols using a borrowing hydrogen method

Despite the limited success of copper-catalyzed alkylations, (NNS)CuCl proved to be an effective catalyst for the sp3 C-H alkylation of fluorene with alcohols. Various primary alcohols and challenging secondary alcohols were successfully used. The practical applicability of the method was effectively tested with several post-functionalization reactions. This copper-catalyzed alkylation of fluorene involved a borrowing hydrogen mechanism.

Copper-Catalyzed Borrowing Hydrogen Reaction for α-Alkylation of Amides with Alcohols

We report the first example of copper-catalyzed α-alkylation of acetamides with alcohols via a borrowing hydrogen strategy. Catalyzed by the in situ-generated copper particles, acetamides and various substituted benzyl or alkyl alcohols were transformed into functionalized amides in good yields with excellent selectivity. Compared with previous work, this process is simple using commercially available Cu(OAc)2 as a precatalyst, without an additional ligand or a metal complex, and easier. Mechanistic studies revealed that aldehyde and α,β-unsaturated amides were the intermediates of this reaction and also disclosed the role of copper in alcohol dehydrogenation and C═C bond hydrogenation.

LiOtBu-promoted synthesis of bis(3-indolyl)methanes by the alkylation of indoles with alcohols under air

Bis(3-indolyl)methanes (BIMs) are known for their important bioactivities, which include anti-cancer, anti-inflammatory, antibacterial, and antioxidant properties. In this study, we are disclosing a metal catalyst-free synthesis of BIMs in high yields via the alkylation reaction of indoles and alcohols in the presence of lithium tert-butoxide base. Notably, oxygen in air played an important role as an oxidant for the facilitation of this transformation. Interestingly, unactivated aliphatic alcohols could be successfully used as alkylating reagents in the alkylation reactions of indole. Especially, several chemical intermediates detected by GC-MS gave important information about the mechanism insights. This method demonstrated cost and environmental advantages for the development of green processes.

C3-Functionalization of indoles with α-heteroaryl-substituted methyl alcohols

The transition metal-free Cs2CO3/Oxone®-mediated C3-alkylation of indoles proceeds in moderate to high yields with a variety of C4-C7 functionalized indoles and is applicable to 2-, 3- and 4-hydroxymethyl pyridines and related electron-deficient heterocycles, permitting novel late-stage drug functionalizations. Preliminary mechanistic studies support a hydrogen autotransfer-type chain process starting with an initial oxidation of the alcohol to the corresponding aldehyde, followed by a subsequent condensation onto indole and reduction/hydride delivery from another equivalent of the primary alcohol.

Recent advances in C/N-alkylation with alcohols through hydride transfer strategies

This review highlights the most recent reports in three powerful and ever-growing fields of borrowing hydrogen, acceptorless dehydrogenative coupling, and base-mediated hydride transfer strategies; which pave the way for generating reactive intermediates via shuttling hydrogen (or hydride) between starting materials without any need for an external hydrogen source to easily construct more complex structures. There is a thorough focus on diversifying the utility of alcohols for C/N-alkylation leading to the synthesis of branched ketones, alcohols, amines, indols, and 6-membered nitrogen-containing heterocycles such as pyridines and pyrimidines, various transformations with the focus on C-C and C-N bond-forming reactions via metal-based catalysis or metal-free approaches in this context to give a global overview in this area.

Efficient Synthesis of C3-Alkylated and Alkenylated Indoles via Manganese-Catalyzed Dehydrogenation

The catalytic dehydrogenation of alcohols is essential for the sustainable production of valuable products. This provids a new strategy for green organic synthesis in chemical industries. Herein, we describe a manganese-based catalytic system that enables the efficient synthesis of C3-alkylated indoles from benzyl alcohols and indoles via the borrowing hydrogen process. Furthermore, dehydrogenative coupling of 2-arylethanols and indoles yields C3-alkenylated indoles. Meanwhile, reacting 2-aminophenethanol instead of indoles can also obtain the corresponding indole products with high selectivity under the same conditions.

Regio-Selective C3- and N-Alkylation of Indolines in Water under Air Using Alcohols

We disclosed a regio-selective C-H and N-H bond functionalization of indolines using alcohols in water via tandem dehydrogenation of N-heterocycles and alcohols. A diverse range of N- and C3-alkylated indolines/indoles were accessed utilizing a new cooperative iridium catalyst. The practical applicability of this methodology was demonstrated by the preparative-scale synthesis and synthesis of a psychoactive drug, N,N-dimethyltryptamine. A catalytic cycle is proposed based on several kinetic experiments, series of control experiments and density functional theory calculations.