Abstract
Transition-metal-nanoparticles-catalyzed C–H activation/functionalization is a prominent
topic in contemporary research, enabling the functionalization of privileged heterocyclic
scaffolds that hold a significant space in the scientific community due to their immense
applications in materials science and in medicinal, natural product, and agricultural
chemistry. Among transition-metal-based nanoparticles, Pd nanoparticle catalysis has
emerged as the most attractive tool for promoting a wide array of practical synthetic
transformations of heterocycles. In the last few years, the catalytic application
of Pd nanoparticles in C–H functionalization has gained popularity in generating relatively
inaccessible bonds with a high degree of selectivity and efficiency via the activation of surface metal atoms at the nanoscale level. The quantum size effect
of nanoparticles offers a large surface area, with typically many easily accessible
active sites/unit areas. These unique characteristics of nanoparticles are considered
primary factors of enhanced catalytic activity compared to bulk materials. The nanoparticle
catalysts anchored on solid-supports plus unsupported types (e.g., magnetic nanoparticles)
allow easy separation from the reaction mixture, enabling recycling multiple times,
which contributes notably to sustainable management and cost efficiency of a production
process. In the current review, we discuss Pd-nanoparticles-catalyzed C(sp2)–H arylation for the synthesis of functionalized heterocycles, covering literature
reports from 2010 to 2021. The preparation of Pd nanoparticles and the mechanistic
realizations in their corresponding reactions are also explained briefly.
1 Introduction
2 Arylation of Heterocyclic Scaffolds
2.1 Synthesis of Functionalized Indole Derivatives
2.2 Synthesis of Functionalized (Benzo)thiazole/Benzoxazole Derivatives
2.3 Synthesis of Functionalized Triazoles
2.4 Synthesis of Functionalized Pyridines and Related Scaffolds
2.5 Synthesis of Functionalized Furan, Thiophene and N-Methylpyrrole Scaffolds
2.6 Synthesis of Functionalized Multiple Heterocycles via Single-Step Strategies
3 Conclusions
Key words
Pd nanoparticles - binary nanoclusters - solid-support - heterogeneity - C(sp
2)–H arylation - heterocycles - leaching - recoverability and recyclability
