Electrophilic Vinylation of Thiols under Mild and Transition Metal‐Free Conditions

The iodine(III) reagents vinylbenziodoxolones (VBX) were employed to vinylate a series of aliphatic and aromatic thiols, providing E‐alkenyl sulfides with complete chemo‐ and regioselectivity, as well as excellent stereoselectivity. The methodology displays high functional group tolerance and proceeds under mild and transition metal‐free conditions without the need for excess substrate or reagents. Mercaptothiazoles could be vinylated under modified conditions, resulting in opposite stereoselectivity compared to previous reactions with vinyliodonium salts. Novel VBX reagents with substituted benziodoxolone cores were prepared, and improved reactivity was discovered with a dimethyl‐substituted core.     

Hydrogenation of Sulfoxides to Sulfides under Mild Conditions Using Ruthenium Nanoparticle Catalysts

The first demonstration of the hydrogenation of sulfoxides under atmospheric H₂ pressure is reported. The highly efficient reaction is facilitated by a heterogeneous Ru nanoparticle catalyst. The mild reaction conditions enable the selective hydrogenation of a wide range of functionalized sulfoxides to the corresponding sulfides. The high redox ability of RuO_x nanoparticles plays a key role in the hydrogenation.     

Regiospecific N‐Arylation of Aliphatic Amines under Mild and Metal‐Free Reaction Conditions

A transition metal‐free N‐arylation of primary and secondary amines with diaryliodonium salts is presented. Both acyclic and cyclic amines are well tolerated, providing a large set of N‐alkyl anilines. The methodology is unprecedented among metal‐free methods in terms of amine scope, the ability to transfer both electron‐withdrawing and electron‐donating aryl groups, and efficient use of resources, as excess substrate or reagents are not required.     

Electrophilic Vinylation of Thiols under Mild and Transition Metal-Free Conditions

The iodine(III) reagents vinylbenziodoxolones (VBX) were employed to vinylate a series of aliphatic and aromatic thiols, providing E-alkenyl sulfides with complete chemo- and regioselectivity, as well as excellent stereoselectivity. The methodology displays high functional group tolerance and proceeds under mild and transition metal-free conditions without the need for excess substrate or reagents. Mercaptothiazoles could be vinylated under modified conditions, resulting in opposite stereoselectivity compared to previous reactions with vinyliodonium salts. Novel VBX reagents with substituted benziodoxolone cores were prepared, and improved reactivity was discovered with a dimethyl-substituted core.     

Hypervalent‐Iodine‐Mediated Cascade Annulation of Diarylalkynes Forming Spiro Heterocycles under Metal‐Free Conditions

An unusual reaction featuring the cascade annulation of internal alkynes to afford spiro heterocycles as the products has been realized for the first time with a hypervalent iodine reagent as the only oxidant. This unprecedented process encompasses not only two sequential C?N/C?O‐bond formations, but also the insertion of a carbonyl oxygen, all in one pot under metal‐free conditions.     

Trifluoromethyl Sulfoxides: Reagents for Metal‐Free C−H Trifluoromethylthiolation

Trifluoromethyl sulfoxides are a new class of trifluoromethylthiolating reagent. The sulfoxides engage in metal‐free C?H trifluoromethylthiolation with a range of (hetero)arenes. The method is also applicable to the functionalization of important compound classes, such as ligand derivatives and polyaromatics, and in the late‐stage trifluoromethylthiolation of medicines and agrochemicals. The isolation and characterization of a sulfonium salt intermediate supports an interrupted Pummerer reaction mechanism.     

Reactivity of Hydroxy‐ and Aquo(hydroxy)‐λ3‐iodane–Crown Ether Complexes

We have designed a series of hydroxy(aryl)‐λ³‐iodane–[18]crown‐6 complexes, prepared from the corresponding iodosylbenzene derivatives and superacids in the presence of [18]crown‐6, and have investigated their reactivities in aqueous media. These activated iodosylbenzene monomers are all non‐hygroscopic shelf‐storable reagents, but they maintain high oxidizing ability in water. The complexes are effective for the oxidation of phenols, sulfides, olefins, silyl enol ethers, and alkyl(trifluoro)borates under mild conditions. Furthermore, hydroxy‐λ³‐iodane–[18]crown‐6 complexes serve as efficient progenitors for the synthesis of diaryl‐, vinyl‐, and alkynyl‐λ³‐iodanes in water. Other less polar organic solvents, such as methanol, acetonitrile, and dichloromethane, are also usable in some cases.     

Mild and Efficient Deoxygenation of Sulfoxides to Sulfides Using HfCl4/KBH4 System

HfCl₄/KBH₄ was found to be a facile, efficient, convenient, and chemoselective system for the deoxygenation of dialkyl, diaryl, and aryl alkyl sulfoxides, especially for the reduction of dibenzyl sulfoxide to the corresponding sulfides under mild conditions. In addition, the HfCl₄/KBH₄ system could be used in reduction of some other sulfur-bearing substrates to the corresponding sulfides, such as 2,2′-dibenzothiazolyl disulfide, but this reducing system could not reduce sulfolane, diphenyl sulfone, p-toluenesulfonic acid, and p-toluenesulfonyl chloride to their corresponding thiophenols.     

Palladium‐Catalyzed Cross‐Coupling of Unactivated Aryl Sulfides with Arylzinc Reagents under Mild Conditions

Cross‐coupling of general aryl alkyl sulfides with arylzinc reagents proceeds smoothly, even at room temperature or below, with a palladium–N‐heterocyclic carbene (NHC) catalyst. When combined with reactions that are unique to organosulfurs, that is, the S_NAr sulfanylation or Pummerer reaction, the cross‐coupling offers interesting transformations that are otherwise difficult to achieve. An alkylsulfanyl group is preferentially converted whilst leaving the tosyloxy and chloro intact, which expands the variety of orthogonal cross‐coupling.     

Metal‐Free CH Bond Activation of Branched Aldehydes with a Hypervalent Iodine(III) Catalyst under Visible‐Light Photolysis: Successful Trapping with Electron‐Deficient Olefins

Direct acyl radical formation of linear aldehydes (RCH₂‐CHO) and subsequent hydroacylation with electron‐deficient olefins can be effected with various types of metal and nonmetal catalysts/reagents. In marked contrast, however, no successful reports on the use of branched aldehydes have been made thus far because of their strong tendency of generating alkyl radicals through the facile decarbonylation of acyl radicals. Here, use of a hypervalent iodine(III) catalyst under visible light photolysis allows a mild way of generating acyl radicals from various branched aldehydes, thereby giving the corresponding hydroacylated products almost exclusively. Another characteristic feature of this approach is the catalytic use of hypervalent iodine(III) reagent, which is a rare example on the generation of radicals in hypervalent iodine chemistry.     

(OXO)(Phosphine)Ruthenium(IV) Complexes: Oxygen Atom Transfer in the Oxidation of Olefins,Sulfides, Sulfoxides,and Free Phosphines

Kinetic and mechanistic studies of the oxidation of olefins, sulfides, and sulfoxides by [Ru^IV(bpy)₂(O)- (PR₃)](ClO₄)₂ (bpy = 2,2′-bipyridine; R = ethyl or phenyl) complexes have been conducted in both methylene chloride and acetonitrile. In all cases, the rate law shows a first-order dependence on both the concentration of (oxo)ruthenium(IV) species and the target substrate. In addition, product distributions of substrate oxidation exhibit a strong dependence on both the particular phosphine ligand and the solvent utilized in the experiment. On the basis of labelling experimcnts and kinetic evidence, a mechanism is proposed involving a two-electron, oxygen atom insertion into the target substrate. Notably, an (oxidized substrate)ruthenium(II) complex has been isolated and characterized for the oxidation of styrene by the (oxo)(triethylphosphine)ruthenium(IV) complex, where a cyclic voltammogram of this complex displays one quasi-reversible Ru(III)/Ru(II) couple with an E_1/2 = 1.24 V vs SSCE. Kinetic analysis of styrene oxidation indicates that the formation of benzaldehyde from styrene does not occur simply by two sequential two-electron steps. In this regard, alternative mechanisms are discussed.     

Metal‐Free Enantioselective Oxidative Arylation of Alkenes: Hypervalent‐Iodine‐Promoted Oxidative C−C Bond Formation

The enantioselective oxyarylation of (E)‐6‐aryl‐1‐silyloxylhex‐3‐ene was achieved using a lactate‐based chiral hypervalent iodine(III) reagent in the presence of boron trifluoride diethyl etherate. The silyl ether promotes the oxidative cyclization, and enhances the enantioselectivity. In addition, the corresponding aminoarylation was achieved.