Photoinduced Regioselective Olefination of Arenes at Proximal and Distal Sites.

The Fujiwara-Moritani reaction has had a profound contribution in the emergence of contemporary C-H activation protocols. Despite the applicability of the traditional approach in different fields, the associated reactivity and regioselectivity issues had rendered it redundant. The revival of this exemplary reaction requires the development of a mechanistic paradigm that would have simultaneous control on both the reactivity and regioselectivity. Often, the high thermal energy required to promote olefination leads to multiple site functionalizations. To this aim, we established a photoredox catalytic system constituting a merger of palladium/organo-photocatalyst (PC) that forges oxidative olefination in an explicit regioselective fashion with diverse arenes and heteroarenes. Visible light plays a significant role in executing "regioresolved" Fujiwara-Moritani reactions without the requirement of silver salts and thermal energy. The catalytic system is also amenable toward proximal and distal olefination aided by the respective directing groups (DGs), which entails the versatility of the protocol in engaging the entire spectrum of C(sp2)-H olefination. Furthermore, streamlining the synthesis of natural products, chiral molecules, drugs, and diversification through late-stage functionalizations underscore the importance of this sustainable protocol. The photoinduced attainment of this regioselective transformation is mechanistically established through control reactions and kinetic studies.

Ligand-Enabled δ-C(sp3 )-H Borylation of Aliphatic Amines.

Directed C-H functionalization has been realized as a complimentary technique to achieve borylation at a distal position of aliphatic amines. Here, we demonstrated the oxidative borylation at the distal δ-position of aliphatic amines using various borylating agents, a palladium catalyst, and a rightly tuned ligand in the presence of a cheap oxidant. Moreover, an organopalladium δ-C(sp3 )-H-activated intermediate has been isolated and crystallographically characterized to get mechanistic insight.

Ultrasound-Facilitated Direct meta-C-H Functionalization of Arenes: A Time-Economical Strategy under Ambient Temperature with Improved Yield and Selectivity.

The horizon of ultrasound-assistance has been expanded to palladium-catalyzed distal C-H functionalization of arenes. Compared to thermal conditions, operationally simple ultrasound mediated distal C-H functionalization occurred with a shorter reaction time and enhanced reactivity of reactants to give superior yields with improved selectivity both in terms of meta:others and mono:di. A wide variety of meta-functionalizations such as olefination, alkylation, acetoxylation, allylation and cyanation were successfully carried out under ambient temperature.

A direct route to six and seven membered lactones via γ-C(sp3)-H activation: a simple protocol to build molecular complexity.

Lactones comprise a class of valuable compounds having biological as well as industrial importance. Development of a methodology to synthesize such molecules directly from readily available materials such as aliphatic carboxylic acid is highly desirable. Herein, we have reported synthesis of δ-lactones and ε-lactones via selective γ-C(sp3)-H activation. The γ-C-H bond containing aliphatic carboxylic acids provide six or seven membered lactones depending on the olefin partner in the presence of a palladium catalyst. A mechanistic investigation suggests that C-H activation is the rate-determining step. Further transformations of the lactones have been carried out to showcase the applicability of the present strategy.

Ligand-Enabled PdII -Catalyzed Iterative γ-C(sp3)-H Arylation of Free Aliphatic Acid.

C-H functionalization of aliphatic carboxylic acids without attaching exogenous auxiliary has been so far limited at the proximal ß-position. In this work, we demonstrate a ligand enabled palladium catalyzed first regioselective distal γ-C(sp3)-H functionalization of aliphatic carboxylic acids without incorporating an exogenous directing group. Aryl iodides containing versatile functional groups including complex organic molecules are well tolerated with good to excellent yields during the γ-C(sp3)-H arylation reaction. Interestingly, weak coordination of carboxylate group can be further extended for sequential hetero di-arylation. Application of the protocol has been showcased by synthesizing substituted α-tetralone. Mechanistic investigations have been carried out to shed light on the reaction pathway.

Photocatalyzed borylation using water-soluble quantum dots.

The synthesis of arylboronates by Sandmeyer-type reactions in the presence of water still remains a significant challenge. Herein, we report the use of water-soluble MPA-capped quantum dot (QD) photocatalysts for the borylation of diazonium salts in the presence of water. A biphasic system under mild acidic conditions remains critical to prevent decomposition and competitive disulphide bond formation. The present protocol offers a broader scope of substrates and borylating agents. Additionally, this catalytic system offers a significantly high turnover number (TON). The present methodology can effectively distinguish subtle reactivity differences between boronic acids and boronates. Mechanistic investigation suggests an excited-state electron transfer pathway.

Iterative Arylation of Amino Acids and Aliphatic Amines via δ-C(sp3 )-H Activation: Experimental and Computational Exploration.

Directed C-H functionalization has been realized as a complementary tool to the traditional approaches for a straightforward access of non-proteinogenic amino acids; albeit such a process is restricted mostly up to the γ-position. In the present work, we demonstrate the diverse (hetero)arylation of amino acids and analogous aliphatic amines selectively at the remote δ-position by tuning the reactivity controlled by ligands. An organopalladium δ-C(sp3 )-H activated intermediate has been isolated and crystallographically characterized. Mechanistic investigations carried out experimentally in conjunction with computational studies shed light on the difference in the mechanistic picture depending on the substrate structure.