Ru(II)-Catalyzed C-H Hydroxyalkylation and Mitsunobu Cyclization of N-Aryl Phthalazinones

Pd(II)-Catalyzed Three-Component Synthesis of Furo[2,3-d]pyrimidines from β-Ketodinitriles, Boronic Acids, and Aldehydes

A Pd(II)-catalyzed three-component synthesis of 2,4,6-triarylfuro[2,3-d]pyrimidines from β-ketodinitriles, boronic acids, and aldehydes has been developed. The participation of both nitrile (-CN) groups led to the concurrent construction of furo-pyrimidine via the formation of C-C, C═C, C-O, C-N, and C═N bonds. The compounds show excellent photoluminescence properties with absorption maxima ranging from 348 to 387 nm and emission from 468 to 533 nm. The synthetic utility of the protocol was further demonstrated through a few postsynthetic manipulations.

Rhodium(III)-catalyzed C-H alkylation of arylhydrophthalazinediones with α-Cl ketones as sp3-carbon alkylated agents

A Rh(III)-catalyzed C-H bond direct alkylation between 2-arylphthalazine-1,4-diones and α-Cl ketones, which are sp³-carbon synthons, under mild conditions has been disclosed. The corresponding phthalazine derivatives are readily obtained in moderate to excellent yields with a wide range of substrates and high functional group tolerance. The practicality and utility of this method are demonstrated by the derivatization of the product.

Ir(III)-Catalyzed Dual C-H Activation of 2-Aryl Phthalazinediones and 3-Aryl-2H-benzo[e][1,2,4]thiadiazine-1,1-dioxides for the Construction of Spiro-Fused Cyclic Frameworks

An Ir(III)-catalyzed double C-H activation strategy has been developed for the synthesis of highly rigid spiro frameworks by means of ortho-functionalization of 2-aryl phthalazinediones and 2,3-diphenylcycloprop-2-en-1-ones using the Ir(III)/AgSbF₆ catalytic system. Similarly, 3-aryl-2H-benzo[e][1,2,4]thiadiazine-1,1-dioxides undergo smooth cyclization with 2,3-diphenylcycloprop-2-en-1-ones to afford a diverse range of spiro compounds in good yields with excellent selectivity. Additionally, 2-arylindazoles provide the corresponding chalcone derivatives under similar reaction conditions.

Ruthenium(II)-Catalyzed Grignard-Type Nucleophilic Addition of C(sp2)-H Bonds to Unactivated Aldehydes

The Grignard-type nucleophilic addition of C(sp²)-H bonds to aldehydes catalyzed by high-oxidation-state transition metal complexes is limited to activated aldehydes. Herein, we report the first example of Grignard-type nucleophilic addition of C(sp²)-H bonds to unactivated aldehydes catalyzed by high-oxidation-state ruthenium(II). The reaction has mild reaction conditions and good functional group tolerance. The corresponding alcohol products are obtained in good to excellent yields.

Dimeric Manganese-Catalyzed Direct Nucleophilic Addition of C(sp2)-H Bonds to Inert Aldehydes

An efficient direct nucleophilic addition reaction of C(sp²)-H bonds to aldehydes catalyzed by a dimeric manganese has been developed. This reaction has a broad range of substrates, and high yields were also obtained with inert aliphatic aldehydes as substrates. A dimeric Mn₂(CO)₈Br₂ was proven to be a more efficient catalyst precursor than the monomeric Mn(CO)₅Br.

Accessing oxy-functionalized N-heterocycles through rose bengal and TBHP integrated photoredox C(sp3)–O cross-coupling

A C(sp3)–O coupling strategy is described involving tautomerizable N-heterocycles (phthalazinone, pyridne, pyrimidinone and quinoxalinone) carbonyl employing rose bengal as the photocatalyst and TBHP.

Cobalt-Catalyzed Vinylic C-H Addition to Formaldehyde: Synthesis of Butenolides from Acrylic Acids and HCHO

A carboxyl-assisted C-H functionalization of acrylic acids with formaldehyde to give butenolides is described. It is the first time that the addition of an inert vinylic C-H bond to formaldehyde has been achieved via cobalt-catalyzed C-H activation. The unique reactivity of the cobalt species was observed when compared with related Rh or Ir catalysts. γ-Hydroxymethylated butenolides were produced by the treatment of Na₂CO₃ after the catalytic reaction in one pot.

Transition-metal-catalyzed C-H bond activation/functionalization and annulation of phthalazinones

Phthalazinones and their higher congeners are commonly prevalent structural motifs that occur in natural products, bioactive molecules, and pharmaceuticals. In the past few decades, transition-metal-catalyzed reactions have received an overwhelming response from organic chemists as challenging organics and heterocycles could be built with ease. Currently, the synthesis of phthalazinones largely depends on transition-metal catalysis, especially by palladium-catalyzed carbonylation. Further, the dominance of transition-metal catalysts was realized from the phthalazinones viewpoint, as nitrogen and oxygen atoms endowed upon them act as directing groups to facilitate diverse C-H activation/functionalization/annulation reactions. This highlight describes the various synthetic methods used to access phthalazinones and functionalize them by reacting with various coupling partners via chelation assistance strategy involving C(sp²)-H/N-H bond activation in the presence of transition-metal (Rh, Ru, Pd, and Ir) catalysts. The mechanisms of sulfonylation, halogenation, acylmethylation, alkylation, and annulation reactions are discussed.

Direct synthesis of indazole derivatives via Rh(III)-catalyzed C-H activation of phthalazinones and allenes

A novel Rh(III)-catalyzed annulation of phthalazinones or pyridazinones with various allenes was developed, leading to the formation of indazole derivatives bearing a quaternary carbon in moderate to good yields. The targeted products were synthesized via sequential C-H activation and olefin insertion, followed by β-hydride elimination and intramolecular cyclization. The synthetic protocol proceeded efficiently with broad functional group tolerance, high atom efficiency and high Z-selectivity. The practicability of this method was proved by synthetic transformation.

Ru(ii)-Catalyzed C-H addition and oxidative cyclization of 2-aryl quinazolinones with activated aldehydes

The ruthenium(ii)-catalyzed cross-coupling reaction between 2-aryl quinazolinones and activated aldehydes is described. This method enables the site-selective hydroxyalkylation under redox-neutral conditions. Moreover, this protocol provides a facile access to various tetracyclic isoindoloquinazolinones by using Cu(OAc)₂ as an external oxidant via C-H addition and subsequent intramolecular cyclization. A wide substrate scope and a high level of chemoselectivity as well as broad functional group tolerance are observed.

Phthalazinone-Assisted C-H Amidation Using Dioxazolones Under Rh(III) Catalysis

The preparation of phthalazinone derivatives is pivotal for their utilization as pharmaceutical agents and other entities. Herein, we report the phthalazinone-assisted carbon-nitrogen bond forming reaction using dioxazolones as robust amidation sources under Rh(III) catalysis. The broad functional group tolerance and complete site-selectivity are observed. Notably, a series of transformations of synthesized compounds into biologically relevant N-heterocycles demonstrates the applicability of the developed methodology.