Aerobic Acetoxyhydroxylation of Alkenes Co-catalyzed by Organic Nitrite and Palladium

TBN as Organic Redox Cocatalyst for Oxidative Tiffeneau-Demjanov-Type Rearrangement Using O2 as Sole Oxidant

The Tiffeneau-Demjanov-type rearrangement is a ring-expansion reaction involving the cationic rearrangement of cyclic alcohols. The carbocation intermediates can be generated in situ via various means, including Wacker oxidation. In near recent reports on the reinvestiagtions by Wahl et al. (Sietmann, J.; Tenberge, M.; Wahl, J. M. Wacker Oxidation of Methylenecyclobutanes: Scope and Selectivity in an Unusual Setting. Angew. Chem., Int. Ed. 2023, 62, e202215381) and Zhu et al. (Feng, Q.; Wang, Q.; Zhu, J.-P. Oxidative Rearrangement of 1,1-Disubstituted Alkenes to Ketones. Science 2023, 379, 1363-1368), stoichiometric oxidants were involved. In this work, we report the Tiffeneau-Demjanov-type rearrangement can be smoothly promoted by the Pd-TBN cocatalyzed aerobic Wacker oxidation using molecular oxygen as the sole oxidant. tert-Butanol is essential for achieving high yields. Since the first report by Grigg et al. in 1977 (Boontanonda, P.; Grigg, R. J. Palladium (II)-Catalysed Ring Expansion of Methylenecyclobutanes and Related Systems. J. Chem. Soc. Chem. Commun. 1977, 17, 583-584), the five-decade journey of Pd-catalyzed Tiffeneau-Demjanov-type rearrangement returns to the aerobic again.

Alkyl nitrite-enabled palladium-catalyzed terminal selective oxidative cyclization of 4-penten-1-ols

Oxidative cyclization of 4-penten-1-ols using a Pd catalyst and n-BuONO or n-BuONO/p-benzoquinone afforded 3-hydroxy- and 3-methoxytetrahydropyrans via terminal selective nucleophilic attack. The radicals formed from n-BuONO and O2 operate as critical oxidants and ligands for Pd.

Visible-Light-Induced Three-Component Tetrafluoroethyl-heteroarylation of Alkenes with 1,1,2,2-Tetrafluoroethanesulfonyl Chloride and Quinoxalin-2(1H)-ones

1,1,2,2-Tetrafluoroethyl-containing compounds are valuable structures due to their unique physicochemical properties, which have increasing potential application in drug discovery. However, synthetic methods for preparing such compounds are rare. Herein, we report the first use of 1,1,2,2-tetrafluoroethanesulfonyl chloride to introduce the HCF2 CF2 group into organic molecules via a three-component, radical tetrafluoroethyl-heteroarylation of alkenes with readily available quinoxalin-2(1H)-ones. This method provides a new and facile approach for late-stage functionalization of potential biologically active molecules.

tert-Butyl Nitrite as a Twofold Hydrogen Abstractor for Dehydrogenative Coupling of Aldehydes with N-Hydroxyimides

A synthetically practical transition metal/catalyst/halogen-free dehydrogenative coupling of aldehydes with N-hydroxyimides promoted solely by tert-butyl nitrite under mild conditions was developed. tert-Butyl nitrite generates two radicals (^tBuO and NO) and thus works as a twofold hydrogen abstractor. A diverse array of N-hydroxyimide esters were prepared from either aliphatic or aromatic aldehydes. Benzoyl-substituted aldehydes such as 2-oxo-2-phenylacetaldehyde are also suitable.

Iodine-Initiated Dioxygenation of Aryl Alkenes Using tert-Butylhydroperoxides and Water: A Route to Vicinal Diols and Bisperoxides

An environment-friendly and efficient dioxygenation of aryl alkenes for the construction of vicinal diols has been developed in water with iodine as the catalyst and tert-butylhydroperoxides (TBHPs) as the oxidant. The protocol was efficient, sustainable, and operationally simple. Detailed mechanistic studies indicated that one of the hydroxyl groups is derived from water and the other one is derived from TBHP. Additionally, the bisperoxides could be obtained in good yields with iodine as the catalyst, Na₂CO₃ as the additive, and propylene carbonate as the solvent, instead.

Visible light-induced aerobic dioxygenation of α,β-unsaturated amides/alkenes toward selective synthesis of β-oxy alcohols using rose bengal as a photosensitizer

The first visible light-induced aerobic dioxygenation of alkenes for the selective synthesis of β-oxy alcohols was developed using non-toxic rose bengal as a photosensitizer.

Silver-catalyzed nitration/annulation of 2-alkynylanilines for a tunable synthesis of nitrated indoles and indazole-2-oxides

Two new types of silver-catalyzed nitration–annulations of 2-alkynylanilines with tert-butyl nitrite (TBN) were reported, leading to the selective formation of a variety of nitrated indoles and indazole-2-oxides.

Solvent-controlled chemoselective N-dealkylation-N-nitrosation or C-nitration of N-alkyl anilines with tert-butyl nitrite

A metal-free, acid-free and chemoselective N-dealkylation-N-nitrosation or C-nitration of N-alkyl anilines has been developed.

Synthesis of Functionalized Indoles via Palladium-Catalyzed Aerobic Cycloisomerization of o-Allylanilines Using Organic Redox Cocatalyst

A scalable and practical synthesis of functionalized indoles via Pd- ^tBuONO cocatalyzed aerobic cycloisomerization of o-allylanilines is reported. Using molecular oxygen as a terminal oxidant, a series of substituted indoles were prepared in moderate to good yields. The avoidance of hazardous oxidants, heavy-metal cocatalysts, and high boiling point solvents such as DMF and DMSO enables this method to be applied in pharmaceutical synthesis. A practical gram-scale synthesis of indomethacin demonstrates its application potential.

Tuning Regioselectivity of Wacker Oxidation in One Catalytic System: Small Change Makes Big Step

A regioselectivity switchable aerobic Wacker-Tsuji oxidation has been developed using catalytic tert-butyl nitrite as a simple organic redox cocatalyst. By solely switching the solvent, either substituted aldehydes or ketones could be prepared under mild aerobic conditions in good yields, respectively. A mechanistic explanation for the selectivity control is proposed.

B2pin2-Mediated Palladium-Catalyzed Diacetoxylation of Aryl Alkenes with O2 as Oxygen Source and Sole Oxidant

A novel palladium-catalyzed alkene diacetoxylation with dioxygen (O₂) as both the sole oxidant and oxygen source is developed, which was identified by ¹⁸O-isotope labeling studies. Control experiments suggested that bis(pinacolato)diboron (B₂pin₂) played a dominant intermediary role in the formation of a C-O bond. This method performed good functional group tolerance with moderate to excellent yields, which could be successfully applied to the late-stage modification of natural products. Furthermore, an atmospheric pressure of dioxygen enhances the practicability of the protocol.

Cu-Catalyzed Aerobic Oxidative Sulfuration/Annulation Approach to Thiazoles via Multiple Csp3-H Bond Cleavage

A novel and practical Cu-catalyzed aerobic oxidative synthesis of thiazoles was developed. This chemistry for the first time achieved thiazole construction from simple aldehydes, amines, and element sulfur through multiple Csp³-H bond cleavage processes. Molecular oxygen was used as a green oxidant in this oxidative protocol. The substrate scope is broad with the tolerance of aliphatic amines. The mechanistic study might promote the reaction design for a new sulfuration/annulation reaction with readily available element sulfur.

Dual Role of H2O2 in Palladium-Catalyzed Dioxygenation of Terminal Alkenes

A palladium-catalyzed, environmentally friendly dioxygenation reaction of simple alkenes has been developed that enabled rapid assembly of valuable α-hydroxy ketones with high atom economy. Notably, control experiments and ¹⁸O isotope-labeling experiments established that H₂O₂ played a dominant dual role in this transformation.

Chelation versus Non-Chelation Control in the Stereoselective Alkenyl sp2 C-H Bond Functionalization Reaction

A hydroxy group chelation-assisted stereospecific oxidative cross-coupling reaction between alkenes was developed under mild reaction conditions. In the presence of palladium catalyst, the alkenes tethered with hydroxy functionality can couple efficiently with electron-deficient alkenes to form the corresponding multi-substituted olefin products. The hydroxy group on the substrate could play dual roles in reaction, acting as the directing group for alkenyl C-H bond activation and controlling the stereoselectivity of the products.