Domino reactions in water for the stereoselective synthesis of novel spiro dihydro-2′H-[indene-2,3′-thiophen]-1(3H)-ones with three contiguous stereocenters

The domino reactions of (E)-2-(aryl)-2,3-dihydro-1H-inden-1-ones and 1,4-dithiane-2,5-diol in the presence of triethylamine in water stereoselectively afforded a library of 2′-(aryl)-4′-hydroxy-4′,5′-dihydro-2′H-spiro[indene-2,3′-thiophen]-1(3H)-ones. This transformation presumably proceeds via the generation of 2-mercaptoacetaldehyde from 1,4-dithiane-2,5-diol followed by Michael addition–intramolecular aldol sequence with C–C and C–S bond formations and creation of three contiguous stereocenters in a one-pot operation.     

l-Proline-catalyzed three-component domino reactions for the synthesis of highly functionalized pyrazolo[3,4-b]pyridines

A series of novel N,3-dimethyl-5-nitro-1-aryl-1H-pyrazolo[3,4-b]pyridin-6-amines was obtained in good yields from the domino reactions of N-methyl-1-(methylthio)-2-nitroprop-1-en-1-amine, aromatic aldehydes, and 3-methyl-1-aryl-1H-pyrazol-5-amines in ethanol in the presence of green catalyst, l-proline. This transformation involves the formation of two C–C and one C–N bonds leading to the creation of a six-membered ring in a one-pot operation.     

Highly selective acetoxylation of sulfonamides via using phenyliodine(III) diacetate

A highly efficient acetoxylation reaction of N-aryl-arylsulfonamides has been developed, presumably proceeding via the selective functionalization of N-aryl C–H bonds. A stoichiometric amount of PhI(OAc)₂ was generally employed as the oxidation reagent, and various para-acetoxylated sulfonamide derivatives had been generated in excellent yields. This chemistry endowed an economic synthesis of valuable acetoxylated sulfonamides through direct C–O bond formation processes.     

Facile four-component domino reactions for the synthesis of highly functionalized tetrahydroquinolones

The four-component domino reactions of (E)-3-(dimethylamino)-1-arylprop-2-en-1-ones with anilines, aromatic aldehydes, and 1,3-cyclohexanediones in an equimolar ratio in acetic acid afforded functionalized tetrahydroquinolones in good yields. This one-pot transformation involves the formation of two C–C and two C–N bonds in a single synthetic operation.     

Microwave-assisted chemoselective synthesis of novel pyrazolo[3,4-b]thieno[3,4-e]pyridines: substitution induced axial chirality

A microwave-assisted chemoselective synthesis of novel pyrazolo[3,4-b]thieno[3,4-e]pyridines has been achieved via tandem Michael addition–cyclization–tautomerization–oxidative aromatization sequence of reactions. Compounds with ortho-substituted phenyl rings exhibited axial chirality due to restricted rotation around C–C single bond.     

Direct metal-free O-arylation of Biginelli 4-aryl-6-methyl-pyrimidine-2(1H)-one derivatives using diaryliodonium salts

4-Aryl-6-methyl-pyrimidine-2(1H)-one scaffolds of Biginelli type were subjected to C–O cross-coupling reactions using symmetrical diaryliodonium salts under transition metal-free conditions to afford 2-aryloxy pyrimidine derivatives in good to excellent yields.     

Generation of 4-substituted coumarins via C–H bond activation under palladium bromide–copper(I) bromide cooperative catalysis

A palladium bromide and copper(I) bromide co-catalyzed reaction of 4-tosyloxy coumarin with benzo[d]oxazole/oxazole/benzo[d]thiazole via C–H activation is described, which generates 4-substituted coumarins in moderate to good yields. 4-Tosyloxy quinolin-2(1H)-one and 2H-pyran-2-one could be applied in this transformation as well.     

Efficient three-component reactions of α-thiocyanato ketones stereoselectively forming E-3-aroylidene-2-oxindole derivatives

A new three-component reaction of α-thiocyanato ketones under microwave irradiation for the stereoselective synthesis of 25 examples of E-3-aroylidene-2-oxindole derivatives has been described. The domino reaction simultaneously installs C–S and C–C bonds through continuous [3+2] cycloaddition/ring opening of in situ generated 1,3-oxathiolanes/S_N2-type reaction sequence.     

Pd-catalyzed assembly of phenanthridines from aryl ketone O-acetyloximes and arynes through C–H bond activation

Pd-catalyzed annulation of aryne and aryl ketone O-acetyloxime via C–H bond activation was realized. Through the C–H bond activation/insertion/cyclization/elimination reaction sequence, phenanthridines are successfully constructed, providing an attractive strategy to approach substituted heterocycle without preactivation of starting materials.     

Sequential one-pot method for oxy-Michael addition,Heck coupling,and degradation followed by condensation: facile synthesis of 2-benzoxepin-3(1H)-ones

A sequential one-pot intermolecular oxy-Michael addition, intermolecular Heck coupling, and intramolecular degradation (retro-oxy-Michael addition) followed by condensation method has been developed for the synthesis of interesting 2-benzoxepin-3(1H)-ones. Significantly, the 2-benzoxepin-3(1H)-ones form the core quantum of biologically vital natural products. The initial oxy-Michael addition and Heck coupling steps involve a straight forward construction of C–O and C–C bonds, whereas, the final condensation step follows a novel mechanistic path via intramolecular degradation, double bond isomerization, and intramolecular condensation. Notably, a remarkable solvent effect has been observed in-order to promote the final intramolecular condensation.     

Solvent-free Brønsted acid-catalyzed Michael addition of nitrogen- and carbon-containing nucleophiles by ultrasound activation

A new method has been developed for the Michael addition of nitrogen- and carbon-containing nucleophiles to cyclic enones. Using this conjugate addition reaction, a variety of different nucleophiles can react with a range of cyclic enones in the presence of p-toluenesulfonic acid under solvent-free ultrasound irradiation conditions affording the corresponding C–N or C–C adducts in good to excellent yields. Comparatively, performing the reaction under ultrasound irradiation gives higher yields, is more efficient and environmentally benign than performing it at high pressure.     

Palladium-catalyzed direct ortho-acylation through an oxidative coupling of 2-arylbenzothiazoles with benzylic alcohols

An efficient protocol was developed for Pd-catalyzed direct C–H bond acylation by cross-dehydrogenative-coupling of arylbenzothiazoles and benzylic alcohols using tert-butyl hydroperoxide (TBHP) as the oxidant. The acylation reactions exhibit good reactivities and excellent regioselectivity.     

A concise synthesis of (±)-3-deoxyisoaltholactone

The novel styryl lactone analog (±)-3-deoxyisoaltholactone was synthesized in 5 steps from dihydrofuran. An intramolecular vinylsilane–oxocarbenium condensation thus afforded the central cis-fused bicyclic ether array in near quantitative yield as a single stereoisomer.     

Rhodium(III)-catalyzed ring-opening of strained olefins through C–H activation of O-acetyl ketoximes: an efficient synthesis of trans-functionalized cyclopentenes and spiro[2.4]heptenes

An efficient strategy for the stereoselective synthesis of functionalized cyclopentenes and spiro[2.4]heptenes from strained olefins via C–H activation of aryl ketone O-acetyl ketoximes using [RhCl₂Cp^∗]₂ catalyst is described. The results revealed that a wide range of readily accessible aryl and heteroaryl ketoximes are compatible in this method for the ring opening of bicyclic and spirotricyclic olefins.     

One pot four-component reaction for the efficient synthesis of spiro[indoline-3,4′-pyrano[2,3-c]pyrazole]-3′-carboxylate derivatives

A novel one pot protocol has been developed to synthesize various spiro[indoline-3,4′-pyrano[2,3-c]pyrazole]-3′-carboxylate derivatives from the four-component reaction of isatin, malononitrile, hydrazine derivatives and dialkyl acetylenedicarboxylates. In this process two C–C bonds, two C–N bonds and one C–O bond have formed in one pot. The notable features of this protocol are simple and environmentally benign reaction condition, easy isolation of products, applicable to a wide range of readily available starting materials and good yields.     

Ring opening of heterocycles containing a C–N double bond: a simple synthesis of imides promoted by acyl palladium species

A detailed study on the reactivity of various heterocycles, containing a C–N double bond, with acyl palladium species, generated in situ from allyl or benzyl halides and CO, has been performed. While the cyclic imine 2-methyl-1-pyrroline reacted with acyl-palladium intermediates to give a bicyclic β-lactam, other heterocycles containing a C–N double bond conjugated with a heteroatom (O or N), showed a ring-opening reaction leading to functionalized imides with high structural diversity. Such methodology represents a simple and direct way to prepare structurally complex imides. Moreover, a reaction mechanism, involving cationic intermediates, was also proposed.     

Improved synthesis of per-O-acetylated C1 hydroxyglycopyranose and structural study as non-covalent organic framework

An improved method for the synthesis of per-O-acetylated C-1-hydroxyglycopyranose was developed by hydrolysis of per-O-acetylated glycopyranosyl α-chlorides derived from sugars with C-2 axial acetates for example l-rhamnose and d-mannose. 2,3,4-Tri-O-acetyl-α-l-rhamnopyranose crystallized in tetragonal space group I4, a rare phenomenon in carbohydrate literature. The three dimensional packing of the molecule with the help of regular hydrogen bond and C–H···O interactions resulted in the formation of porous framework showing channels with pore size 7 Å.     

Stereocontrolled transformation of cyclohexene β-amino esters into syn- or anti-difunctionalized acyclic β-amino acid derivatives

A stereocontrolled approach to functionalized acyclic β^2,3-amino acid derivatives was accomplished from cis- or trans-2-aminocyclohexenecarboxylates derived from bicyclic β-lactam regioisomers. The transformations were based on oxidative ring cleavage through the ring C–C double bond of the cyclohexene β-amino esters, followed by functionalization of the dialdehyde intermediates with different phosphoranes. This stereospecific and stereocontrolled procedure was applied to the synthesis of acylic β^2,3-amino acid derivatives functionalized with ester, nitrile, keto, alkyl or arylalkyl groups.     

Oxidative C(Sp)–H activation and C–N cleavage of N-methyl amines under transition-metal-free condition for synthesis of methylene-bridged bis-1,3-diketones

A transition-metal-free oxidative methylenation reaction was developed. Methylene-bridged bis-1,3-dicarbonyl compounds were synthesized by oxidative C(Sp³)–H activation and C–N cleavage of N-methyl amines. This novel reaction avoids the use of transition metal catalyst. Furthermore, the reaction are very mild and operational convenient.     

On the mechanism of Pd(0)-catalyzed coupling of propargylic carbonates with N-tosylhydrazones: density functional theory survey

In this article, we have theoretically investigated the possible reaction mechanisms for Pd(0)-catalyzed coupling of propargylic carbonates with N-tosylhydrazones. The ωb97X-D method and C-PCM solvent model are used to describe the reaction processes. After the formation of allenylpalladium through C–O bond cleavage from propargylic carbonates, both decarboxylation and ligand exchange processes are explored. Then, depending on different conditions, we considered three possible types of reaction mechanisms, carbene insertion triggered by N₂ release, C–C coupling reactions without N₂ release, and C–C coupling reactions via the out-sphere attack of diazo compound. Our results indicate that it is favorable to undergo the carbene insertion into allenylpalladium after ligand exchange with diazo compound, which is partially agreement with the experimental suggestions. Although the decarboxylation is more difficult than ligand exchange, the reaction rate could be limited by Pd-catalyzed N₂ dissociation from diazo compound. Additionally, it should be essential to select DFT-D method to describe this reaction.