Palladium-Catalyzed Distal m-C-H Functionalization of Arylacetic Acid Derivatives

Synthesis of Aryl Naphthoquinones and Maleimides via Pd(II)-Catalyzed Template-Assisted m-C(sp2)-H Functionalization Reaction

An efficient approach for the synthesis of substituted aryl naphthoquinones via a Pd(II)-catalyzed template-assisted m-C(sp2)-H bond functionalization reaction of arylmethane sulfonates have been demonstrated. The method involves usage of less expensive and abundant pharmacologically important scaffold naphthoquinone. A wide range of arylmethane sulfonates were examined and found to be compatible with the protocol. The protocol has also been further extended to the synthesis of various substituted aryl maleimide scaffolds. A plausible reaction mechanism has also been proposed to account for the selective distal m-C(sp2)-H bond functionalization reaction.

Aliphatic Nitrile Template Enabled meta-C-H Olefination of Indene Enoate Esters under Microwave Accelerating Conditions

Site-selective activation of a particular remote C-H bond in molecules with multiple C-H bonds remains challenging in organic synthesis. In addition, evolving such transformations via the utilization of unconventional techniques is highly desirable. We demonstrated hitherto unexplored double bond geometry-guided and end-on nitrile-template-assisted meta-C-H functionalization of indene enoate esters under microwave-accelerated conditions. Significantly, the strategy exhibited broad compatibility concerning the substrates and olefin coupling partners. Remarkably, drug diversification has also been showcased.

Distal-C-H Functionalization of Biphenyl Scaffolds Assisted by Easily Removable/Recyclable Aliphatic Nitrile Templates

We present here the distal-C-H activation/functionalization of biphenyl scaffolds using aliphatic nitrile templates. The approach has demonstrated good to exclusive meta selectivities over a wide range of olefination and acetoxylation substrates. In addition, bis-olefination has been accomplished in a one-pot, sequential manner. Notably, this technique highlights the diversification of pharmaceuticals and natural products. Consequently, the temporary directing aliphatic template has been recovered quantitively from the coupled product.

A Cheap and Efficient Oxidant (n-Bu)4NNO3-Enabled C(sp2)- and C(sp3)-H Olefination at Room Temperature

To further promote the widely practical application of C-H activation, developing green and mild reaction conditions has invariably been the objective of researchers, especially when it comes to remote C-H activation reactions. Herein, we report a new cheap and powerful (n-Bu)₄NNO₃ oxidant. This oxidant is efficient and universal for Pd(II)-catalyzed sp² and sp³ C-H olefination and allows the reaction to be carried out at room temperature. Because of this, we attempted to make C-H functionalization more economical and environmentally benign.

Directing group assisted rhodium catalyzed meta-C-H alkynylation of arenes

Site-selective C-H alkynylation of arenes to produce aryl alkynes is a highly desirable transformation due to the prevalence of aryl alkynes in various natural products, drug molecules and in materials. To ensure site-selective C-H functionalization, directing group (DG) assisted C-H activation has been evolved as a useful synthetic tool. In contrast to DG-assisted ortho-C-H activation, distal meta-C-H activation is highly challenging and has attracted significant attention in recent years. However, developments are majorly focused on Pd-based catalytic systems. In order to diversify the scope of distal meta-C-H functionalization, herein we disclosed the first Rh(i) catalyzed meta-C-H alkynylation protocol through the inverse Sonogashira coupling reaction. The protocol is compatible with various substrate classes which include phenylacetic acids, hydrocinnamic acids, 2-phenyl benzoic acids, 2-phenyl phenols, benzyl sulfonates and ether-based scaffolds. The post-synthetic modification of meta-alkynylated arenes is also demonstrated through DG-removal as well as functional group interconversion.

Recyclable Aliphatic Nitrile-Template Enabled Remote meta-C-H Functionalization at Room Temperature

This article describes the development of a new aliphatic nitrile-template-directed remote meta-selective C-H olefin functionalization reaction of arenes. Remarkably, unlike the previous reports, this process is feasible at room temperature and enabled the formation of products with excellent regioselectivity. The present protocol encompasses a broad spectrum of substituted dihydrocinnamic acids and olefins, producing meta-C-H olefinated products (up to 96% yield). In addition, the efficacy of the present method has been showcased by the synthesis of various drug analogues (e.g., cholesterol, estrone, ibuprofen, and naproxen). Significantly, the robustness of meta-olefination was also demonstrated by gram-scale synthesis. The new nitrile-based meta-directing template, in particular, could be easily synthesized in two steps and recycled under mild conditions.