Palladium-Catalyzed Ring-Opening Reaction of Cyclopropenones with Vinyl Epoxides.

We report herein the Pd-catalyzed selective ring-opening reaction of cyclopropenones with vinyl epoxides. By using a commercially available Pd2(dba)3·CHCl3-BINAP catalyst, a wide range of conjugated alkadienyl carboxylates could be accessed in good yield and excellent regioselectivity. The new application of zwitterionic π-allyl palladium intermediates has been demonstrated in organic synthesis.

Metal-Free Synthesis of Aryl Selenocyanates and Selenaheterocycles with Elemental Selenium.

This work reports a green method for the synthesis of aryl selenocyanates via a three-component reaction of arylboronic acids, Se powder, and trimethylsilyl cyanide (TMSCN) under metal-free and additive-free conditions. Remarkably, TMSCN acts as not only the substrate, but also the catalyst. Various selenaheterocycles can be also accessed with a catalytic amount of TMSCN.

α-Selective C(sp3)-H Thio/Selenocyanation of Ketones with Elemental Chalcogen.

A facile method is disclosed for the synthesis of α-thio/selenocyanato ketones through regioselective C-H thio/selenocyanation of ketones. The advantages include the use of easily available starting materials, high efficiency, simple operation, and easy scale-up. Control experiments provide evidence that the reaction proceeded via a radical way, while kinetic isotope effect experiments reveal that the cleavage of the C-H bond serves as the rate-limiting step.

Palladium-catalyzed coupling reaction of 2-iodobiphenyls with alkenyl bromides for the construction of 9-(diorganomethylidene)fluorenes.

An atom economical protocol for the construction of 9-(diorganomethylidene)fluorenes through palladium-catalyzed coupling reactions of 2-iodobiphenyls with alkenyl bromides has been reported. The reaction proceeds through the C-H activation/oxidative addition/reduction elimination/intramolecular Heck coupling reaction to afford a series of 9-(diorganomethylidene)fluorenes with good yields. Control experiments demonstrate that a five-membered palladacycle acts as a key intermediate and ß-H elimination serves as the rate-limiting step.

Ag2O-promoted ring-opening reactions of cyclopropenones with oximes.

Ag2O-promoted ring-opening reactions of cyclopropenones with oximes is disclosed in this work, providing a direct route to 1,3-oxazinones. This method highlights a new reactivity of cyclopropenones which undergo 1,4-addition with oximes followed by ß-carbon elimination to in situ generate a α-carbonyl ketene intermediate.

Deselenylative Acylation and Nitration of Monoselenides.

A deselenylative protocol that enables the construction of the C-C and C-N bonds has been disclosed. By using acyl chloride/AgOTf as an efficient acylation reagent, diarylselenides smoothly undergo deselenylative acylation to produce a series of aroyl compounds. In addition, deselenylative nitration can be enabled by a mild nitration reagent consisting of TsCl and AgNO3, furnishing a diverse array of nitroaromatic compounds.

Transition-metal-free four-component reaction of nitriles and disulfides/diselenides.

One-pot synthesis of structurally diverse sulfurized/selenated 4-aminopyrimidines has been reported via t-BuOK/K2S2O8-promoted four-component reaction of mixed nitriles and disulfides/diselenides. Mechanistic studies indicate that the reaction proceeds through radical and ionic pathways, and an alkenyl sulfide serves as a key intermediate.

An (NH4)2S2O8-promoted cross-coupling of thiols/diselenides and sulfoxides for the synthesis of unsymmetrical disulfides/selenosulfides.

An (NH4)2S2O8-promoted cross-coupling of thiols/diselenides and sulfoxides to construct unsymmetrical disulfides/selenosulfides is disclosed. Control experiments demonstrate that (NH4)2S2O8 acts as an acid and an oxidant, while both ionic and radical routes are involved in the reaction. The KIE experiments reveal that C-H bond cleavage of sulfoxides was involved in the turnover-limiting step.

Cascade Ring-Opening Dual Halogenation of Cyclopropenones with Saturated Oxygen Heterocycles.

Represented is a CuX2- or I2-promoted ring-opening dual halogenation of cyclopropenones with saturated oxygen heterocycles, providing an efficient method for the synthesis of 3-haloacrylates. The ring-opening reaction enables the construction of two C-X (X = Cl, Br, or I) bonds and a C-O bond as well as the cleavage of two C-O bonds and a C-C bond in a single step. This protocol is highly atom economical, has an excellent substrate scope, and exhibits the ability for gram-scale reaction.

Selective [3 + 2] Cycloaddition of Cyclopropenone Derivatives and Elemental Chalcogens.

A highly efficient method is disclosed for the synthesis of 1,2-dichalcogen heterocycles via [3 + 2] cycloaddition of cyclopropenone derivatives and elemental chalcogens. Different from other cyclopropenone derivatives, cyclopropenselenones undergo unprecedented rearrangement with elemental sulfur. The features of this protocol include mild reaction conditions, high efficiency, excellent atom economy, gram-scale ability, and good regioselectivity.

Synthesis of selenated isochromenones by AgNO3-catalyzed three-component reaction of alkynylaryl esters, selenium powder and ArB(OH)2.

Reported is the AgNO3-catalyzed three-component reaction of alkynylaryl esters, selenium powder and ArB(OH)2, providing a facile entry to selenated isochromenones. This work highlights the use of selenium powder as a selenium reagent in the synthesis of selenated isochromenones for the first time.

Efficient synthesis of 2-aryl-2H-indazoles by base-catalyzed benzyl C-H deprotonation and cyclization.

A straightforward and efficient method for the preparation of 2-aryl-2H-indazoles from ortho-alkyl substituted azoxybenzenes is presented. The reaction proceeds through base-catalyzed benzyl C-H deprotonation and cyclization to afford 2-aryl-2H-indazoles in good yields. This synthetic strategy can be applied to the construction of several fluorescent and bioactive molecules.

Three-Component Reactions of Alkynone o-Methyloximes, Element Selenium, and Boronic Acids Leading to 4-Organoselenylisoxazoles.

We report an Ag-catalyzed one-pot three-component reaction of alkynone o-methyloxime, element selenium, and boronic acid, providing a facile route to selenated isoxazole product. This protocol features high efficiency, wide substrate scope, and the use of selenium powder as the selenium source.

3-Methyl-sulfanyl-5-phenyl-4H-1,2,4-triazol-4-amine-water (6/1).

In the title compound, 6C(9)H(10)N(4)S·H(2)O, the dihedral angle between the five-membered triazole ring and the phenyl ring is 44.33 (16)°. The solvent water molecule is disordered about a special position with symmetry and its occupancy cannot be greater than 0.1667. The crystal structure is stabilized by inter-molecular N-H⋯N and C-H⋯N hydrogen bonds.

Selenium Radical Mediated Cascade Cyclization: Concise Synthesis of Selenated Benzofurans (Benzothiophenes).

Presented in this work is a novel methodology for the synthesis of selenated benzofurans (or benzothiophenes) via AgNO2-catalyzed radical cyclization of 2-alkynylanisoles (or 2-alkynylthioanisoles), Se powder, and arylboronic acids. This method enables the construction of a benzofuran (benzothiophene) ring, two C-Se bonds, and a C-O(S) bond as well as the cleavage of a C-O(S) bond in a single step. Preliminary mechanistic studies imply that the AgNO2-catalyzed cyclization proceeds via an aryl selenium radical intermediate.

Photoinduced Hydroxylation of Organic Halides under Mild Conditions.

Presented in this paper is photoinduced hydroxylation of organic halides, providing a mild access to a range of functionalized phenols and aliphatic alcohols. These reactions generally proceed under mild reaction conditions with no need for a photocatalyst or a strong base and show a wide substrate scope as well as excellent functional group tolerance. This work highlights the unique role of NaI that allows a challenging transformation to proceed under mild reaction conditions.

Direct synthesis of 3-acylbenzothiophenes via the radical cyclization of 2-alkynylthioanisoles with α-oxocarboxylic acids.

A radical cascade cyclization of 2-alkynylthioanisoles with α-oxocarboxylic acids with AgNO3 has been described. This reaction provides a novel route to directly access 3-acylbenzothiophenes from simple chemical feedstocks. In particular, the utility of the approach was demonstrated by its application to the synthesis of a polymerization inhibitor and a raloxifene precursor.

Transition-Metal-Free Highly Chemoselective and Stereoselective Reduction with Se/DMF/H2O System.

A novel metal-free reduction system, in which H2Se (or HSe-) produced in situ from Se/DMF/H2O acts as the active reducing species, has been developed. By using water as an inexpensive, safe, and environmentally friendly surrogate as the hydrogen donor, this new reduction system incorporating Se/DMF/H2O displayed high selectivity and good activity in the reduction of α,ß-unsaturated ketones and alkynes. Therefore, this reduction system has great potential to be a general and practical reduction methodology in organic transformation.