Improved Synthesis of 2,2‐Arylmethylene Bis(3‐hydroxy‐5,5‐dimethyl‐2‐cyclohexene‐1‐one) and 1,8‐Dioxo‐octahydroxanthene Derivatives Catalyzed by Electrogenerated Base and Sulfuric Acid

An efficient method has been developed for the synthesis of 1,8‐dioxo‐octahydroxanthene derivatives in two‐step. In the first step, the electrogenerated base (EGB) catalyzed multicomponent transformation of dimedone and aromatic aldehydes in an undivided cell in the presence of sodium bromide as an electrolyte into 2,2′‐arylmethylene bis(3‐hydroxy‐5,5‐dimethyl‐2‐cyclohexene‐1‐one) at room temperature. In the second step, H₂SO₄ was employed as a dehydrating reagent for the cyclization process to give symmetrical heterocycles 1,8‐dioxo‐octahydroxanthene derivatives. Short reaction time, convenient work up, and using of inexpensive reagents, simple equipment, novel and eco‐friendly procedure make this strategy more useful for the preparation of xanthene derivatives.     

Efficient Synthesis of (−)‐Corynoline by Enantioselective Palladium‐Catalyzed α‐Arylation with Sterically Hindered Substrates

Sterically hindered substrates can be employed in an enantioselective palladium‐catalyzed α‐arylation with the chiral monophosphorus ligand BI‐DIME. This process enabled an efficient synthesis of the antidepressant (S)‐nafenodone, a four‐step enantioselective synthesis of the Sceletium alkaloid (+)‐sceletium A‐4, a concise five‐step enantioselective synthesis of (?)‐corynoline, as well as a three‐step preparation of (?)‐DeN‐corynoline.     

One‐Step Synthesis of 1‐(4,5‐Diphenylpyrimidin‐2‐yl)thiourea

A simple and straightforward methodology toward the synthesis of novel 1‐(4,5‐diphenylpyrimidin‐2‐yl)thiourea has been developed by a one‐step reaction of isoflavones with amidinothiourea. A series of 16 new compounds was synthesized. All compounds were characterized by FT‐IR, NMR, and elemental analysis. The structure of a typical compound was established by X‐ray diffraction. A variety of substrates can participate in the process with good yields and high purities, making this methodology suitable for library synthesis in drug discovery.     

Synthesis and Characterization of 3‐(5‐(Fluorodinitromethyl)‐1H‐1,2,4‐triazol‐3‐yl)‐4‐nitrofurazan: A Novel Promising Energetic Component of Boron‐based Fuels for Rocket Ramjet Engines

The synthesis of a new energetic 1,2,4‐triazole compound bearing nitrofurazanyl and fluorodinitromethyl units, which may find use as a component for rocket ramjet engines (RRE), is described. The target product was prepared in a four‐step process applying oxidation/nitration/decarboxylation/fluorination reactions and is fully characterized. Its density and structural features were uniquely determined by X‐ray analysis. It is shown that replacing HMX with the compound of this study in boron‐based fuels gives an increase in energy.     

Palladium‐Catalyzed Intramolecular CH Difluoroalkylation: Synthesis of Substituted 3,3‐Difluoro‐2‐oxindoles

The synthesis of 3,3‐difluoro‐2‐oxindoles through a robust and efficient palladium‐catalyzed C? H difluoroalkylation is described. This process generates a broad range of difluorooxindoles from readily prepared starting materials. The use of BrettPhos as the ligand was crucial for high efficiency. Preliminary mechanistic studies suggest that oxidative addition is the rate‐determining step for this process.     

Synthesis of substituted 3‐(5‐amino‐[1,3,4]thiadiazol‐2‐yl)‐2H‐pyrano[2,3‐c]pyridin‐2‐ones

An efficient two‐step synthesis of novel 3‐(5‐amino‐[1,3,4]thiadiazol‐2‐yl)‐2H‐pyrano[2,3‐c]pyridine‐2‐ones was developed. In the first step, a new 2H‐pyrano[2,3‐c]pyridine‐3‐carboxamide 5 was prepared by Knoevenagel condensation of pyridoxal hydrochloride with cyanoacetamide. In the second step, the reaction of carboxamide 5 with a series of N⁴‐substituted thiosemicarbazides yielded a library of 35 dis crete compounds 8 {1–35} in high yields. The intermolecular recyclization mechanism leading to these products is discussed.     

Palladium‐Catalyzed Intramolecular C?H Difluoroalkylation: Synthesis of Substituted 3,3‐Difluoro‐2‐oxindoles

The synthesis of 3,3‐difluoro‐2‐oxindoles through a robust and efficient palladium‐catalyzed C H difluoroalkylation is described. This process generates a broad range of difluorooxindoles from readily prepared starting materials. The use of BrettPhos as the ligand was crucial for high efficiency. Preliminary mechanistic studies suggest that oxidative addition is the rate‐determining step for this process.     

Synthesis of 1,4‐Cyclohexanedimethanol, 1,4‐Cyclohexanedicarboxylic Acid and 1,2‐Cyclohexanedicarboxylates from Formaldehyde,Crotonaldehyde and Acrylate/Fumarate

Valuable polyester monomers and plasticizers—1,4‐cyclohexanedimethanol (CHDM), 1,4‐cyclohexanedicarboxylic acid (CHDA), and 1,2‐cyclohexanedicarboxylates—have been prepared by a new strategy. The synthetic processes involve a proline‐catalyzed formal [3+1+2] cycloaddition of formaldehyde, crotonaldehyde, and acrylate (or fumarate). CHDM is produced after a subsequent hydrogenation step over a commercially available Cu/Zn/Al catalyst and a one‐pot hydrogenation/oxidation/hydrolysis process yields CHDA, whereas 1,2‐cyclohexanedicarboxylate is obtained by a Pd/C‐catalyzed tandem decarbonylation/hydrogenation step.     

Synthesis of 1,4‐Cyclohexanedimethanol, 1,4‐Cyclohexanedicarboxylic Acid and 1,2‐Cyclohexanedicarboxylates from Formaldehyde,Crotonaldehyde and Acrylate/Fumarate

Valuable polyester monomers and plasticizers—1,4‐cyclohexanedimethanol (CHDM), 1,4‐cyclohexanedicarboxylic acid (CHDA), and 1,2‐cyclohexanedicarboxylates—have been prepared by a new strategy. The synthetic processes involve a proline‐catalyzed formal [3+1+2] cycloaddition of formaldehyde, crotonaldehyde, and acrylate (or fumarate). CHDM is produced after a subsequent hydrogenation step over a commercially available Cu/Zn/Al catalyst and a one‐pot hydrogenation/oxidation/hydrolysis process yields CHDA, whereas 1,2‐cyclohexanedicarboxylate is obtained by a Pd/C‐catalyzed tandem decarbonylation/hydrogenation step.     

Three‐Step Synthesis of 3‐Aryl‐2‐sulfanylthieno[2,3‐b]‐, ‐[2,3‐c]‐, or ‐[3,2‐c]pyridines from the Corresponding Aryl(halopyridinyl)methanones

A convenient three‐step procedure for the synthesis of three types of 3‐aryl‐2‐sulfanylthienopyridines 4, 8 , and 12 has been developed. The first step of the synthesis of thieno[2,3‐b]pyridine derivatives 4 is the replacement of the halo with a (sulfanylmethyl)sulfanyl group in aryl(2‐halopyridin‐3‐yl)methanones 1 by successive treatment with Na₂S?9 H₂O and chloromethyl sulfides to give aryl{2‐[(sulfanylmethyl)sulfanyl]pyridin‐3‐yl}methanones 2 . In the second step, these were treated with LDA (LiNⁱPr₂) to give 3‐aryl‐2,3‐dihydro‐2‐sulfanylthieno[2,3‐b]pyridin‐3‐ols 3 , which were dehydrated in the last step with SOCl₂ in the presence of pyridine to give the desired products. Similarly, thieno[2,3‐c]pyridine and thieno[3,2‐c]pyridine derivatives, 8 and 12 , respectively, can be prepared from aryl(3‐chloropyridin‐4‐yl)methanones 5 and aryl(4‐chloropyridin‐3‐yl)methanones 9 , respectively.     

Synthesis and antimicrobial activity of 5,5′‐dimethyl‐2‐oxido‐[1,3,2]‐dioxaphos‐phorinane‐2‐yl‐amino carboxylates

Synthesis of several 5,5‐dimethyl‐2‐oxido‐[1,3,2]‐dioxaphosphorinane‐2‐yl‐amino carboxylates ( 4a–j ) was accomplished through a two‐step process. This involves prior preparation of the intermediate monochloride ( 2 ), 2‐chloro‐5,5‐dimethyl [1,3,2]dioxaphosphorinane‐2‐oxide and its subsequent reaction with various amino acid esters ( 3a–j ) in dry tetrahydrofuran in the presence of triethyl amine at room temperature. They were characterized by elemental analysis, IR, ¹H, ¹³C, ³¹P NMR, and mass spectral data. Their antifungal and antibacterial activity is also evaluated. Majority of these compounds exhibited moderate antimicrobial activity in the assay. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:256–260, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20426     

Photochemistry of 1‐Cyclopropyl‐6‐fluoro‐1,4‐dihydro‐4‐oxo‐7‐ (piperazin‐1‐yl)quinoline‐3‐carboxylic Acid (=Ciprofloxacin) in Aqueous Solutions

The 1‐cyclopropyl‐6‐fluoro‐1,4‐dihydro‐4‐oxo‐7‐(piperazin‐1‐yl)quinoline‐3‐carboxylic acid (=ciprofloxacin; 1 ) undergoes low‐efficiency (Φ=0.07) substitution of the 6‐fluoro by an OH group on irradiation in H₂O via the ππ* triplet (detected by flash photolysis, λ_max 610 nm, τ 1.5 μs). Decarboxylation is a minor process (≤5%). The addition of sodium sulfite or phosphate changes the course of the reaction under neutral conditions. Reductive defluorination is the main process in the first case, while defluorination is accompanied by degradation of the piperazine moiety in the presence of phosphate. In both cases, the initial step is electron‐transfer quenching of the triplet (k_q=2.3⋅10⁸M ⁻¹ s⁻¹ and 2.2⋅10⁷M ⁻¹ s⁻¹, respectively). Oxoquinoline derivative 1 is much more photostable under acidic conditions, and in this case the F‐atom is conserved, and the piperazine group is stepwise degraded (Φ=0.001).     

Rapid Access to 2‐Methylene Tetrahydrofurans and γ‐Lactones: A Tandem Four‐Step Process

A one‐pot tandem process involving hydrolysis, Knoevenagel condensation, Michael addition, and Conia‐ene (HKMC) reactions has been developed for the rapid synthesis of indanone‐fused 2‐methylene tetrahydrofurans from the reaction of enynals and propynols. In this process, two rings and four bonds are generated with 100 % atom‐economy and high step‐efficiency. The resulting tetrahydrofurans were readily oxidized into α‐methylene γ‐lactones, which are one of the most important substructures in natural and bioactive compounds.     

Visible‐Light‐Promoted Generation of α‐Ketoradicals from Vinyl‐bromides and Molecular Oxygen: Synthesis of Indenones and Dihydroindeno[1,2‐c]chromenes

Ortho‐alkynylated α‐bromocinnamates can be converted by a visible‐light‐mediated photocascade reaction with molecular oxygen into either indenones or dihydroindeno[1,2‐c]chromenes. The one‐step process features key photochemical steps, that is, the initial activation of vinyl bromides through energy transfer to give α‐ketoradicals in a reaction with molecular oxygen, followed by α‐oxidation of an arene moiety by 6‐π electrocyclization, and subsequent hydroxylation by an electron‐transfer process from the same photocatalyst leads to the dihydroindeno[1,2‐c]chromenes.     

Two‐step Synthesis of New γ‐Lactones via Cyclization of 7‐Chloro‐2‐(methoxycarbonyl)‐4‐6‐dimethylocta‐(2E,4E,6E)‐trienoic acid

A new rapid synthesis of γ‐lactones, cis fused with a cyclopentenic ring by thermal cyclization of 7‐chloro‐2‐(methoxycarbonyl)‐4‐6‐dimethylocta‐7‐phenyl (or methyl) (2E,4E,6E)‐trienoic acids was reported. The key step implicates an intramolecular cyclization to a cyclopentenyl cation, according to an electrocyclic π_2s + π_2a conrotatory process, published in a recent paper (from the corresponding diacids). We have investigated the thermal behavior of the corresponding half‐esters since; if the cyclization obeys to the proposed mechanism, the diacids, half‐esters must also cyclize in a similar manner. Saponification of these led to γ‐dilactones via intermediary cyclopropanes. Mechanistic pathways were investigated.     

An Efficient Synthesis of 3‐(3‐benzyl‐2‐(phenylimino)‐2,3‐dihydrothiazol‐4‐yl)‐6‐methyl‐4‐(2‐oxo‐2‐phenylethoxy)‐3,4‐dihydro‐2H‐pyran‐2‐one Derivatives via Multi‐Component Approach

An easy, highly efficient and a new convenient one‐pot, two‐step approach to the synthesis of 3‐(3‐benzyl‐2‐(phenylimino)‐2,3‐dihydrothiazol‐4‐yl)‐6‐methyl‐4‐(2‐oxo‐2‐phenylethoxy)‐3,4‐dihydro‐2H‐pyran‐2‐one is described. These compounds were synthesized from 3‐(3‐benzyl‐2‐(phenylimino)‐2,3‐dihydrothiazol‐4‐yl)‐4‐hydroxy‐6‐methyl‐3,4‐dihydro‐2H‐pyran‐2‐one and α‐bromoketones in good yields. The compounds 4 were synthesized by a multi‐component reaction between 1 , 2 , and 3 and the prominent features of this protocol are mild reaction conditions, operation simplicity, and good to high yields of products.     

Folding Dynamics of 10‐Residue β‐Hairpin Peptide Chignolin

Short peptides that fold into β‐hairpins are ideal model systems for investigating the mechanism of protein folding because their folding process shows dynamics typical of proteins. We performed folding, unfolding, and refolding molecular dynamics simulations (total of 2.7 μs) of the 10‐residue β‐hairpin peptide chignolin, which is the smallest β‐hairpin structure known to be stable in solution. Our results revealed the folding mechanism of chignolin, which comprises three steps. First, the folding begins with hydrophobic assembly. It brings the main chain together; subsequently, a nascent turn structure is formed. The second step is the conversion of the nascent turn into a tight turn structure along with interconversion of the hydrophobic packing and interstrand hydrogen bonds. Finally, the formation of the hydrogen‐bond network and the complete hydrophobic core as well as the arrangement of side‐chain–side‐chain interactions occur at approximately the same time. This three‐step mechanism appropriately interprets the folding process as involving a combination of previous inconsistent explanations of the folding mechanism of the β‐hairpin, that the first event of the folding is formation of hydrogen bonds and the second is that of the hydrophobic core, or vice versa.     

Synthesis of 1‐Amino‐5,6‐diaryl‐3‐cyano‐1H‐pyridin‐2‐ones and 6,7‐Diaryl‐4‐cyano‐3‐hydroxy‐1H‐[1,2]diazepines from Isoflavones

The one‐step cyclocondensation of substituted isoflavones (=3‐phenyl‐4H‐1‐benzopyran‐4‐ones) with cyanoacetohydrazide in the presence of KOH afforded a mixture of 1‐amino‐5,6‐diaryl‐3‐cyano‐1H‐2‐pyridin‐2‐ones and 6,7‐diaryl‐4‐cyano‐3‐hydroxy‐1H‐[1,2]diazepines.     

A simple synthesis of 5‐ethoxycarbonyl‐6‐phenyl‐1,3‐dioxin‐4‐ones and ethyl 3‐benzoyl‐4‐oxo‐2,6‐diphenylpyran‐5‐carboxylate

4‐Ethoxycarbonyl‐5‐phenyl‐2,3‐dihydrofuran‐2,3‐dione 1 reacts with aldehydes via the acylketene intermediate 2 giving the 1,3‐dioxin‐4‐ones 3a‐e and the 1,4‐bis(5‐ethoxycarbonyl‐4‐oxo‐6‐phenyl‐4H‐1,3‐dioxin‐2‐yl)benzene 4 , and a one step reaction between dibenzoylmethane and oxalylchloride gave 3,5‐dibenzoyl‐2,6‐diphenyl‐4‐pyrone 7 . The reaction of 1 with dibenzoylmethane, a dicarbonyl compound, provided ethyl 3‐benzoyl‐4‐oxo‐2,6‐diphenylpyran‐5‐carboxylate derivative 9 . Compound 9 was converted into the corresponding ethyl 3‐benzoyl‐4‐hydroxy‐2,6‐diphenylpyridine‐5‐carboxylate derivative 10 via its reaction with ammonium hydroxyde solution in 1 ‐butanol.     

Facile synthesis of 5‐aryl‐1‐[(arylamino)methyl]‐ 1,3,5‐triazinane‐2‐thiones

A series of 5‐aryl‐1‐arylaminomethyl‐1,3,5‐triazinane‐2‐thiones has been prepared in a one‐step procedure from condensation of readily available aromatic amines with thiourea and formaldehyde. A mechanism is presented to account for the formation of the products. The overall sequence provides a simple and efficient route to prepare in good to excellent yields and in a short experimental time. J. Heterocyclic Chem., (2012).