Dihydrobenzofuran is an important skeleton for bioactive compounds and natural products. Hydroquinones can be easily modified into substituted hydroquinones, which effectively undergo oxidation to produce the corresponding benzoquinone derivatives. Benzoquinones are reactive electrophiles that are frequently utilized in coupling with olefins to dihydrobenzofurans. Herein, we report the one-pot oxidative coupling of hydroquinones bearing an electron-withdrawing group at the C2 position with olefins to dihydrobenzofurans in the presence of the Lewis acidic FeCl3 and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) oxidant. Furthermore, this method was applied to the oxidative coupling of N-electron-withdrawing group-substituted 4-aminophenol.

Catechols possessing electron-withdrawing groups at the C3 position effectively underwent oxidative functionalization at the C4 position in the presence of phenyliodine(III) diacetate (PIDA) and heteroarene nucleophiles (e.g., indole, indazole, and benzotriazole) to produce the corresponding biaryl products. The PIDA-mediated oxidation of catechol derivatives afforded the ortho-benzoquinone intermediate, which subsequently underwent regioselective nucleophilic addition to the α,β-unsaturated carbonyl moiety of ortho-benzoquinone using indole, indazole, and benzotriazole to give 4-substituted catechol derivatives in a one-pot manner. Notably, the nucleophilic substitution positions of indazole and benzotriazole were perfectly controlled. Additionally, the reaction using N-methylaniline as the nucleophile afforded a tertiary amine product.

BACKGROUND: Oxidation is a valuable tool in preparative organic chemistry. Oxoammonium salts and nitroxides have proven valuable as reagents and catalysts in this endeavor.
OBJECTIVE: The objective of this study is to scale up the oxidative amidation, ester formation, and nitrile formation using nitroxide as an organocatalyst.
METHODS: Oxidative functionalization reactions were scaled from the 1 mmol to the 1 mole level. Sodium persulfate was used as the primary oxidant, and a nitroxide was employed as a catalyst. The products of the reactions were isolated in analytically pure form by extraction with no need for column chromatography.
RESULTS: The oxidative amidation and esterification of aldehydes can be scaled up from 1 mmol to 1 mole effectively, with comparable product yields being obtained at each increment. This work shows that conditions developed on a small scale can be transferred to a larger scale without reoptimization. The oxidative functionalization of aldehydes to prepare nitriles is not amenable to direct scale-up due to the concomitant formation of significant quantities of the corresponding carboxylic acid, thereby compromising the product yield.
CONCLUSIONS: Two of the three oxidative transformations studied here can be scaled up successfully from the 1 mmol to the 1 mole level.

This account describes our recent work on developing guanidinium hypoiodite- catalysts for oxidative carbon-nitrogen and carbon-carbon bond-forming reactions. These reactions proceeded smoothly using guanidinium hypoiodite generated in situ by treating 1,3,4,6,7-hexahydro-2H-pyrimido[1,2-a]pyrimidine hydroiodide salts with an oxidant. In this approach, the ionic interaction and hydrogen bonding ability of the guanidinium cations enable bond-forming reactions that have been difficult with conventional methods. Enantioselective oxidative carbon-carbon bond-forming reaction was also achieved by using a chiral guanidinium organocatalyst.

This article deals with isomeric ruthenium complexes [RuIII (LR )2 (acac)] (S=1/2) involving unsymmetric β-ketoiminates (AcNac) (LR =R-AcNac, R=H (1), Cl (2), OMe (3); acac=acetylacetonate) [R=para-substituents (H, Cl, OMe) of N-bearing aryl group]. The isomeric identities of the complexes, cct (cis-cis-trans, blue, a), ctc (cis-trans-cis, green, b) and ccc (cis-cis-cis, pink, c) with respect to oxygen (acac), oxygen (L) and nitrogen (L) donors, respectively, were authenticated by their single-crystal X-ray structures and spectroscopic/electrochemical features. One-electron reversible oxidation and reduction processes of 1-3 led to the electronic formulations of [RuIII (L)(L⋅ )(acac)]+ and [RuII (L)2 (acac)]- for 1+ -3+ (S=1) and 1- -3- (S=0), respectively. The triplet state of 1+ -3+ was corroborated by its forbidden weak half-field signal near g≈4.0 at 4 K, revealing the non-innocent feature of L. Interestingly, among the three isomeric forms (a-c in 1-3), the ctc (b in 2 b or 3 b) isomer selectively underwent oxidative functionalization at the central β-carbon (C-H→C=O) of one of the L ligands in air, leading to the formation of diamagnetic [RuII (L)(L\')(acac)] (L\'=diketoimine) in 4/4\'. Mechanistic aspects of the oxygenation process of AcNac in 2 b were also explored via kinetic and theoretical studies.

Oxidative alkene difunctionalization reactions are important in synthetic organic chemistry because they can install polar functional groups onto simple non-polar alkene moieties. Many of the most common methods for these reactions rely upon the reactivity of pre-oxidized electrophilic heteroatom donors that can often be unstable, explosive, or difficult to handle. Herein, we describe a method for alkene oxyamination and diamination that utilizes simple carbamate and urea groups as nucleophilic heteroatom donors. This method uses a tandem copper-photoredox catalyst system that is operationally convenient. The identity of the terminal oxidant is critical in these studies. Ag(I) salts proved to be unique in their ability to turn over the copper cocatalyst without deleteriously impacting the reactivity of the organoradical intermediates.

The iodo-oxyimidation of styrenes with the N-hydroxyimide/I2/hypervalent iodine oxidant system was proposed. Among the examined hypervalent iodine oxidants (PIDA, PIFA, IBX, DMP) PhI(OAc)2 proved to be the most effective; yields of iodo-oxyimides are 34-91%. A plausible reaction pathway includes the addition of an imide-N-oxyl radical to the double C=C bond and trapping of the resultant benzylic radical by iodine. It was shown that the iodine atom in the prepared iodo-oxyimides can be substituted by various nucleophiles.

The observation of an unexpected oxidative rearrangement coupling reaction led to the development of a novel method for the efficient functionalization of tetrahydro-β-carbolines (THβCs). The treatment of THβCs with photogenerated singlet oxygen (1 O2 ) afforded unstable dioxetanes, which underwent further transformation to form new bonds in the presence of trifluoroacetic acid. This operationally simple protocol exhibits broad functional-group tolerance and is suitable for the late-stage functionalization of complex druglike molecules.