One-Pot Synthesis of 3-Substiuted Indoles from 2-(2-Nitro-1-phenylethyl)cyclohexanone Derivatives

Recent Advances in Sequentially Pd-Catalyzed One-Pot Syntheses of Heterocycles

Sequential Pd-catalyzed one-pot synthetic methodologies have emerged as a powerful and versatile approach in organic synthesis, enabling the construction of complex heterocyclic architectures with high efficiency, selectivity, and atom economy. This review discusses key advancements in multistep, sequentially Pd-catalyzed one-pot processes for accessing heterocyclic derivatives, focusing on classic reactions like Suzuki-Miyaura, Sonogashira, Heck, and hydroamination and extending to specialized techniques such as directed C-H activation. The concatenation of these steps has advanced the scope of one-pot strategies. A section is dedicated to exploring the cooperative use of palladium with other metals, particularly copper, ruthenium, and gold, which has broadened the range of accessible heterocyclic derivatives. Highlighted applications include the synthesis of biologically and pharmaceutically relevant compounds, such as tris(hetero)aryl systems, spiro-oxindoles, and indole derivatives. These one-pot strategies not only streamline synthesis but also align with green chemistry principles by minimizing purification steps and reducing waste and energy consumption. The review also addresses current challenges and limitations in these methodologies, offering insights into ongoing efforts to optimize reaction conditions and expand the applicability of sequential Pd-catalyzed processes.

RuII-Catalyzed C-H Activated Diverse Cyclization with Transformation of Substrate-DG to Functional Groups: Synthesis of Functionalized Indoles and Indenones

We present an elegant and efficient method for Ru(II)-catalyzed C-H activation, followed by a diverse range of intermolecular cross-dehydrogenative coupling reactions. This process is facilitated by an intrinsic directing group (DG) and includes the in situ transformation of the DG into common and useful functional groups. Notably, this method avoids the installation and deinstallation of the directing group. Our approach enables the selective functionalization of benzimidate, coupled with the cyclization of o-alkynyl-aniline, resulting in the high-yield synthesis of diverse compounds such as indoles, and indenones. The sequential formation of C-N, C-C, and C-O bonds, followed by hydrolysis, underscores the versatile in situ transformation of the directing group. This work not only broadens the synthetic toolbox for constructing complex heterocyclic structures but also highlights the potential for sustainable and selective synthesis of valuable compounds.

Synthesis of Branch-Type 3-Allylindoles from N-Alkyl-N-cinnamyl-2-ethynylaniline Derivatives Using π-Allylpalladium Chloride Complex as a Catalyst

The reaction of N-alkyl-N-cinnamyl-2-ethynylaniline derivatives 1 via annulation and aza-Claisen-type rearrangement easily afforded corresponding branch-type 3-allylindoles 2 with high regioselectivities in good yields using π-allylpalladium chloride complex as a catalyst.

Synthesis of 2-(Pyridin-2-yl)phenols and 2-(Pyridin-2-yl)anilines

Herein, we report a new synthetic strategy for 2-(pyridin-2-yl)phenols and 2-(pyridin-2-yl)anilines catalyzed by a Pd/C-ethylene system. The starting materials, 2-(pyridin-2-yl)cyclohexan-1-ones, can be easily prepared by the reaction of substituted pyridine N-oxide and cyclohexanones. The most useful feature of this method is that both 2-(pyridin-2-yl)phenols and 2-(pyridin-2-yl)anilines are easily synthesized independently using the same compound as a starting material, simply by adding or not adding a nitrogen source.