Generation of alkyl and acyl radicals by visible-light photoredox catalysis: direct activation of C-O bonds in organic transformations.

Alkyl and acyl radicals play a critical role in the advancement of chemical synthesis. The generation of acyl and alkyl radicals by activation of C-O bonds using visible-light photoredox catalysis offers a mild and environmentally benign approach to useful chemical transformations. Alcohols, carboxylic acids, anhydrides, xanthates, oxalates, N-phthalimides, and thiocarbonates are some examples of alkyl and acyl precursors that can produce reactive radicals by homolysis of the C-O bond. These radicals can then go through a variety of transformations that are beneficial for the construction of synthetic materials that are otherwise difficult to access. This study summarizes current developments in the use of organic photocatalysts, transition-metal photoredox catalysts, and metallaphotocatalysts to produce acyl and alkyl radicals driven by visible light.

Ruthenium-catalyzed dehydrogenative cyclization to synthesize polysubstituted 4-quinolones under solvent-free conditions.

Herein, we describe acridine-based SNS-Ru pincer-catalysed unprecedented dehydrogenative annulation of alcohols with 2'-aminoacetophenone to synthesize 2,3-disubstituted-4-quinolones. The developed protocol was utilized with a wide range of alcohols with various aminoacetophenones. To expand the synthetic utility, 4-quinolones with antibiotic properties were synthesized and various important post-synthetic modifications of the synthesized scaffolds were performed. Various control experiments were performed to understand the mechanism, which showed that C-alkylation has the edge over N-alkylation and referred to the possibility of in situ alkenylation to branched ketones.

Progressive study on ruthenium catalysis for de(hydrogenative) alkylation and alkenylation using alcohols as a sustainable source.

At present, alcohols are considered sustainable starting materials that can be used in organic synthesis for various organic transformations and the preparation of commodity chemicals. Acceptorless dehydrogenation (AD) and borrowing hydrogen (BH) are two important methods for activating alcohols for alkenylation and alkylation. These approaches are sustainable because their process liberates water and in some cases (i.e., AD) molecular hydrogen as clean byproducts. Moreover, this area of research has attracted significant attention in the catalysis community, and various transition metals have been used to explore the same. Herein, in this review, we focus on the development of Ru-based catalyst systems for C-alkylation/alkenylation reactions via the AD or BH approach. This review also features a comparative study of the various Ru-catalysts used to optimize the reaction conditions. Furthermore, we extensively cover the outcomes of the mechanistic studies to describe the reaction pathways.

Ru Doped Hydrotalcite Catalyzed Borrowing Hydrogen-Mediated N-Alkylation of Benzamides, Sulfonamides, and Dehydrogenative Synthesis of Quinazolinones.

An efficient Ru doped hydrotalcite catalyzed N-alkylation of benzamides and sulfonamides with alcohols via borrowing hydrogen catalysis is illustrated. Various primary alcohols, including benzyl, heteroaryl, and aliphatic alcohols, were alkylated in good to excellent yields. To shed light on the mechanistic details, several control studies and deuterium labeling experiments were performed. Mechanistic studies underpin that the reaction is going via a borrowing hydrogen pathway rather than an SN1 type mechanism. The reaction can be easily scaled up without any detrimental effect on the yield. The catalyst is also capable of synthesizing quinazolinone directly from 2-aminobenzamide and alcohols. Successful recyclability and high reactivity highlight the practical applicability of the catalyst.

Acceptorless dehydrogenative construction of C[double bond, length as m-dash]N and C[double bond, length as m-dash]C bonds through catalytic aza-Wittig and Wittig reactions in the presence of an air-stable ruthenium pincer complex.

The construction of C[double bond, length as m-dash]N bonds was achieved by the dehydrogenative coupling of alcohol and azide via aza-Wittig type reaction. The reaction is catalyzed by an acridine-derived ruthenium pincer complex and does not use any oxidant. The present protocol offers a wide substrate scope, including aliphatic, aryl or heteroaryl alcohol/azides. This expeditious protocol was successfully applied to construct a C[double bond, length as m-dash]C bond directly from alcohol via dehydrogenative Wittig reaction. Furthermore, the synthesis of structurally important pyrrolo[1,4]benzodiazepine derivatives was also achieved by this methodology.