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.

Cobalt-catalyzed cross-electrophile coupling of alkynyl sulfides with unactivated chlorosilanes

Herein, we disclose a highly efficient cobalt-catalyzed cross-electrophile alkynylation of a broad range of unactivated chlorosilanes with alkynyl sulfides as a stable and practical alkynyl electrophiles. Strategically, employing easily synthesized alkynyl sulfides as alkynyl precursors allows access to various alkynylsilanes in good to excellent yields. Notably, this method avoids the utilization of strong bases, noble metal catalysts, high temperature and forcing reaction conditions, thus presenting apparent advantages, such as broad substrate scope (72 examples, up to 97% yield), high Csp-S chemo-selectivity and excellent functional group compatibility (Ar-X, X = Cl, Br, I, OTf, OTs). Moreover, the utilities of this method are also illustrated by downstream transformations and late-stage modification of structurally complex natural products and pharmaceuticals. Mechanistic studies elucidated that the cobalt catalyst initially reacted with alkynyl sulfides, and the activation of chlorosilanes occurred via an SN2 process instead of a radical pathway.

Cationic and Neutral PdII and PtII Pincer Complexes of Phosphinamino-Triazolyl-Pyridine [PN(H)N]: Pincer Ligand-Stabilized Palladium Nanoparticles and Their Catalytic Annulation of Internal Alkynes to Indenones

We describe the synthesis of a triazolyl-pyridine-based aminophosphine, N-(diphenylphosphaneyl)-6-(1-phenyl)-1H-(1,2,3-triazol-4-yl)pyridine-2-amine [2,6-{(PPh₂)-N(H)(C₅H₃N)(C₂HN₃C₆H₅)}] [1, PN(H)N hereafter], and its palladium and platinum complexes and their catalytic application. The reaction of 1 with [M(COD)Cl₂] (M = Pd or Pt) afforded the cationic complex [(MCl){PN(H)N}-κ³-P,N,N]Cl [M = Pd (2) or Pt (3)]. Alternatively, compounds 2 and 3 were also synthesized by treating [2,6-{H₂N(C₅H₃N)(C₂HN₃C₆H₅)}] (A) with [M(COD)Cl₂] (M = Pd or Pt), followed by the addition of stoichiometric amounts of PPh₂Cl and Et₃N. The neutral, dearomatized complexes [(MCl){PNN}-κ³-P,N,N] [M = Pd (4) or Pt (5)] were prepared by the deprotonation of the NH of 2 and 3 with 1 equiv of ^tBuOK. Compounds 4 and 5 were also synthesized stepwise by treating [2,6-{H₂N(C₅H₃N)(C₂HN₃C₆H₅)}] (A) with [M(COD)Cl₂] (M = Pd or Pt) to give intermediate complexes [{MCl₂}2,6-{NH₂(C₅H₃N)(C₂HN₃C₆H₅)-κ²-N,N}] [M = Pd (B) or Pt (C)], which were subsequently phosphinated. The in situ-generated PNN ligand-stabilized Pd nanoparticles from compound 2 catalyzed the annulation of o-bromobenzaldehyde with alkynes to yield indenone derivatives. Mechanistic investigations suggested that the reaction was catalyzed by Pd nanoparticles (Pd@2) generated from compound 2 and proceeded through sequential oxidative addition, alkyne insertion, and reductive elimination steps to produce indanone products.

Nickel-Catalyzed Sodium Hypophosphite-Participated Direct Hydrophosphonylation of Alkyne toward H-Phosphinates

The traditional methods for the synthesis of phosphinate esters use phosphorus trichloride (PCl₃) as the phosphorous source, resulting in procedures that are often highly polluting and energy intensive. The search for an alternative approach that is both mild and environmentally friendly is a challenging, yet highly rewarding task in modern chemistry. Herein, we use an inorganic phosphorous-containing species, NaH₂PO₂, to serve as the source of phosphorous that participates directly in the nickel-catalyzed selective alkyne hydrophosphonylation reaction. The transformation was achieved in a multicomponent fashion and at room temperature, and most importantly, the H-phosphinate product generated is an advanced intermediate which can be readily converted into diverse phosphinate derivatives, including those bearing new P-C, P-S, P-N, P-Se, and P-O bonds, thus providing a complimentary method to classic phosphinate ester synthesis techniques.

Iron-Promoted Oxidative Alkylation/Cyclization of Ynones with 4-Alkyl-1,4-dihydropyridines: Access to 2-Alkylated Indenones

An iron-promoted oxidative tandem alkylation/cyclization of ynones with 4-alkyl-substituted 1,4-dihydropyridines for the efficient synthesis of 2-alkylated indenones is described. The process occurs via oxidative homolysis of a C-C σ-bond in 1,4-dihydropyridines to generate an alkyl radical followed by the addition of C-C triple bonds in ynones and intramolecular cyclization. A wide range of alkyl radicals could be efficiently transferred to generate a series of synthetically useful 2-alkylated indenones with excellent selectivity under mild conditions.

Transition-metal-free approaches to 2,3-diarylated indenones from 2-alkynylbenzaldehydes and phenols with tunable selectivity

The first transition-metal-free regioselective synthesis of 2,3-diarylindenones via tandem annulation of 2-alkynylbenzaldehydes with phenols is described. Two different modes of reaction controlled by electronic effects and temperature furnished either "non-rearranged" or "rearranged" indenones in high selectivity.

Recursive Anion-Triggered Tandem Reactions of ortho-Bis-ynones: Tunable Synthesis of 1-Indenones and Cyclopenta[a]inden-8(2H)-ones

Recursive anion-mediated activation of o-bis-ynones sets off a Michael addition-aldol reaction-dehydrative rearrangement cascade, leading to the one-pot synthesis of 1-indenones via orthogonal interplay between the two ortho-ynone moieties. Repeating the recursive anion engagement with the 1-indenones unfolded access to a functionally embellished cyclopenta[a]inden-8(2H)-one core and its spiroannulated analogues either directly or stepwise through tandem 1,6-Michael-type addition-6π electrocyclization and an in situ oxidation sequence.

Mechanochemical Solvent-Free Synthesis of Indenones from Aromatic Carboxylic Acids and Alkynes

The mechanochemical solvent-free synthesis of indenones from aromatic carboxylic acids and alkynes was achieved through triflic anhydride (Tf₂O)-induced cyclization reaction. A variety of indenones including a bioactive PPARγ agonist were obtained in up to 90% yield at room temperature. The present protocol has the advantages of mild reaction conditions, high reaction efficiency, and feasibility of scalable synthesis, providing a facile and sustainable route to diverse indenones.

Ni-Catalyzed electrophile driven regioselective arylative cyclization of ortho-functional diaryl acetylenes for the synthesis of pyridine and indene derivatives

A regioselective arylative cyclization of ortho functional diaryl acetylenes for the synthesis of selectively substituted diaryl pyridine and indene derivatives is accomplished through an electrophile driven alkyne polarization.

Metal-free cascade rearrangement/radical addition/oxidative C–H annulation of propargyl alcohols with sodium sulfinates: access to 2-sulfenylindenones

A facile protocol for the construction of 2-sulfenylindenones via one-pot cascade rearrangement/radical addition/oxidative C–H cyclization of propargyl alcohols with sodium sulfinates has been developed.

Water-assisted metal-free catalyzed cyclization of 2-alkynylarylketones: a facile approach to indenones

A facile approach starting from 2-alkynylarylketones was developed for the construction of functionalized indenones under metal-free and water-assisted conditions.