Synthesis of Spiro[piperidine‐3,3′‐oxindoles] via Gold(I)‐Catalyzed Dearomatization of N‐Propargyl‐ and N‐Homoallenyl‐2‐bromotryptamines

N‐Propargyl‐ and N‐homoallenyl‐2‐bromo‐β‐tryptamines undergo gold(I)‐catalyzed dearomatizing cyclizations to afford 2‐bromospiroindolenines that are in situ hydrolyzed to furnish spirooxindoles in a one‐pot process. Tryptophane derivatives (R²=CO₂Et) led upon cyclization to chiral spirooxindoles in excellent diastereoselectivities.

     

Synthesis of Quinolines by Visible‐Light Induced Radical Reaction of Vinyl Azides and α‐Carbonyl Benzyl Bromides

A visible‐light induced radical reaction of vinyl azides and α‐carbonyl benzyl bromides was developed, which provides an efficient route to polysubstituted quinolines via a C C and C N bond formation sequence.

     

An Efficient Catalytic Chromium‐Mediated Iodocyclopropanation Reaction: Stereoselective Synthesis of Iodocyclopropanecarboxamides

A catalytic chromium‐mediated novel synthesis of iodocyclopropanecarboxamides is reported. This reaction can be carried out on aromatic (E)‐ or (Z)‐α,β‐unsaturated amides in which the CC double bond is di‐ or trisubstituted. This process takes place with total stereospecificity and the new C I stereogenic center is generated with high stereoselectivity. Some synthetic applications of the obtained iodocyclopropanecarboxamides are also reported. The structures of the iodocyclopropanes and derivatives were established by X‐ray analysis.     

Organocatalytic Diels–Alder Reaction of 2‐Vinylindoles with Methyleneindolinones: An Efficient Approach to Functionalized Carbazolespirooxindoles

An unprecedented asymmetric Diels–Alder reaction of 2‐vinylindoles with methyleneindolinones has been disclosed. Under bifunctional organocatalysis by cinchona‐derived squaramide catalyst, a series of diversely functionalized carbazolespirooxindole derivatives bearing three contiguous stereocenters are rapidly constructed under mild conditions (48–90% yields, up to >20:1 dr and 99% ee).

     

Gold(I)‐Catalyzed [4+2] Annelation/Nucleophilic Addition Sequence: Stereoselective Synthesis of Functionalized Bicyclo[4.3.0]nonenes

The gold(I)‐catalyzed isomerization of readily available 1,8‐dien‐4‐ynes allows the rapid construction of a variety of synthetically useful bicyclo[4.3.0]nonenes by a stereoselective sequence involving a [4+2] annelation/nucleophilic addition process.     

Stereoselective Synthesis of Pyrroloquinolines by a Brønsted Acid Catalyzed [4+2]‐Heterocyclization of Indole‐7‐Carbaldehydes,Anilines and Electron‐Rich Alkenes

The pyrrolo[3,2,1‐ij]quinoline heterocyclic core is found in the structure of a variety of compounds with interesting applications and then, new efficient and flexible strategies to construct this skeleton are required. Here, a new diastereoselective tetrafluoroboric acid (HBF₄)‐catalyzed three‐component coupling reaction of 1H‐indole‐7‐carbaldehyde derivatives, anilines and electron‐rich alkenes to give pyrrolo[3,2,1‐ij]quinolines is described. The reaction involves an unusual [4+2]‐heterocyclization between an in situ formed imine and an alkene. The new catalytic method, where water is the only by‐product, is efficient, robust and flexible, and allows for multigram‐scale synthesis.

     

Tunable Phosphine‐Mediated Domino Reaction: Selective Synthesis of 2,3‐Dihydrofurans and Biaryls

We have developed a novel strategy to control the product distribution between 2,3‐dihydrofurans and biaryls from the same starting materials by tuning the catalytic or stoichiometric process. By controlling the loading of the phosphine PR₃, the Morita–Baylis–Hillman carbonates can be selectively used as a C₁ or a C₃ synthon, respectively. This investigation has given new insights into tunable domino reactions and will be useful in diversity‐oriented synthesis (DOS).     

A Rapid and Efficient Synthesis of Quinone Derivatives: Ru(II)‐ or Ir(I)‐Catalyzed Hydrogen Peroxide Oxidation of Phenols and Methoxyarenes

Hydroquinone and methoxybenzene derivatives were catalytically oxidized promptly to the corresponding quinones in up to 99% yield. With a catalyst loading of 0.01 mol %, a maximum TON of 8.4×10³ was attained in the case of Ru(II)‐complex. Ru(II)(pybox‐dh)(pydic) is able to enhance the hydrogen peroxide oxidation of substituted hydroquinones as well as methoxybenzenes, but Ir[(coe)₂Cl]₂ and Ir[(cod)Cl]₂ were found to be effective catalysts only for the former substrates under similar oxidation conditions.     

A Practical Asymmetric Synthesis of Enantiopure Spiro[4,4]nonane‐1,6‐dione

A practical asymmetric synthesis of enantiopure spiro[4,4]nonane‐1,6‐dione, a valuable precursor for chiral ligand development, is reported. This synthetic strategy includes a kinetic resolution of the readily synthesized ketone precursor with a chiral quaternary carbon center by bioreduction with baker’s yeast as the key step, followed by a hydroformylation, oxidation, esterification and Dieckmann cyclization reaction sequence to generate the spiro five‐membered ring. It was found that the masking of the β‐ketone carbonyl group of enantiopure ethyl 1‐allyl‐2‐oxocyclopentanecarboxylate via formation of a ketal with 1,3‐diol derivative is necessary during the process of Dieckmann condensation in order to prevent its racemization under basic conditions. This method allows the gram‐scale preparation of both enantiomers of spiro[4,4]nonane‐1,6‐dione ( 1 ) with excellent enantiopurities (up to >99% ee) in the overall yields of 54% [(R)‐ 1 ] and 42% [(S)‐ 1 ], respectively. The practicality of the present synthetic procedure has provided a fundamental platform for the development of spiro[4,4]nonane‐1,6‐dione‐based chiral chemistry.     

Practical Synthesis of Chiral N,N′‐Bis(2′‐pyridinecarboxamide)‐1,2‐cyclohexane Ligands

A simple and scalable procedure for the preparation of chiral ligands 1 and 2 from trans‐1,2‐diaminocyclohexane and 2‐picolinic acid is described.     

Copper‐Catalyzed Trifluoromethylation of Aliphatic N‐Arylhydrazones: A Concise Synthetic Entry to 2‐Trifluoromethylindoles from Simple Aldehydes

The copper‐catalyzed C(sp²) H trifluoromethylation of N,N‐disubstituted hydrazones using the Togni reagent is demonstrated to proceed efficiently for aliphatic aldehyde‐derived substrates. The success of the reactions relied on the choice of the N,N‐diphenylamino group as the terminal hydrazone amino group where N,N‐dialkylamino groups were preferred for (hetero)aromatic aldehyde‐derived substrates. In addition, the trifluoromethylated N‐arylhydrazones are shown to be ideal substrates for Fischer indole synthesis allowing a straightforward, three‐step access to 2‐trifluoromethylindole derivatives from simple aldehydes.

     

Silver‐Catalyzed One‐Pot Cyclization Reaction of Electron‐ Deficient Alkynes and 2‐Yn‐1‐ols: An Efficient Domino Process to Polysubstituted Furans

Transition metal‐catalyzed domino reactions have been used as powerful tools for the preparation of polysubstituted furans in a one‐pot manner. In this paper, an efficient synthetic method was developed for the construction of tri‐ or tetrasubstituted furans from electron‐deficient alkynes and 2‐yn‐1‐ols by a silver‐catalyzed domino reaction. It is especially noteworthy that a 2,3,5‐trisubstituted 4‐ynyl‐furan was formally obtained in an extremely direct manner without tedious stepwise synthesis. In addition, regio‐isomeric furans were observed when substituted aryl alkynyl ketones were employed. This methodology represents a highly efficient synthetic route to electron‐deficient furans for which catalytic approaches are scarce. The reaction proceeds efficiently under mild conditions with commercially available catalysts and materials.     

Potential Energetic Plasticizers on the Basis of 2,2‐Dinitropropane‐1,3‐diol and 2,2‐Bis(azidomethyl)propane‐1,3‐diol

Different carboxylic acid derivatives of 2,2‐dinitropropane‐1,3‐diol (DNPD) and 2,2‐bis(azidomethyl)propane‐1,3‐diol (BAMP) were synthesized to investigate their suitability as energetic plasticizers. The syntheses were carried out using acyl chlorides of acetic, propionic, and butyric acid. The obtained products were characterized by elemental analysis, NMR, and IR spectroscopy. The energetic properties of the synthesized compounds were calculated on the basis of the computed heats of formation at the CBS‐4M level of theory using the EXPLO5 version 6.02 computer code. Investigations of physical stabilities were carried out using BAM drop hammer and friction tester. Low and high temperature behavior was determined by differential scanning calorimetry (DSC). The energetic and physical properties of the synthesized compounds were compared to the literature known energetic plasticizers N‐butyl nitratoethylnitramine (BuNENA) and diethylene glycol bis(azidoacetate) ester (DEGBAA). For analyzing the plasticizing abilities, mixtures of glycidyl azide polymer (GAP) and poly(3‐nitratomethyl‐3‐methyloxetan) (polyNIMMO) were prepared with both propionyl based compounds in different ratios and investigated regarding their glass transition temperatures and viscosity. Both compounds showed plasticizing effects in the range of BuNENA.     

Nitrative Spirocyclization Mediated by TEMPO: Synthesis of Nitrated Spirocycles from N‐Arylpropiolamides,tert‐Butyl Nitrite and Water

A new method for the nitrative spirocyclization of alkynes is described. This method involves the oxidative difunctionalization of alkynes initiated by a radical attack pathway using t‐BuONO (tert‐butyl nitrite) combined with water as the nitro source and TEMPO [(2,2,6,6‐tetramethyl‐piperidin‐1‐yl)oxyl] as the initiator, and it represents a new example of oxidative alkyne difunctionalization via the formation of C N/C C bonds for the assembly of nitroalkene unit‐containing spirocycles.

     

Synthesis of 4‐Aryl‐2(5H)‐furanones by Gold(I)‐Catalyzed Intramolecular Annulation

A novel method that involves intramolecular annulation and a new type of rearrangement has been developed for the synthesis of 4‐aryl‐2(5H)‐furanones. A variety of prop‐2‐ynyl 3‐oxo‐3‐phenylpropanoates undergo annulation cyclization in the presence of chloro(triphenylphosphine)gold and trifluoromethanesulfonic to afford the desired products in moderate to high yields.     

Gold(I)‐Catalyzed Carboaminations of Allenes by N‐Allyltetrahydro‐β‐carbolines: An Experimental and Theoretical Study

N‐Allyltetrahydro‐β‐carbolines bearing a pendant allene undergo unprecedented gold(I)‐catalyzed cyclizations proceeding with an allyl migration from the nitrogen to the allene moiety. The initial product of the gold‐catalyzed cyclization evolves either via isomerization or Cope rearrangement, leading to different scaffolds. Density function theory (DFT) calculations established that the allyl migration occurs in an asynchronous suprafacial manner.

     

Controlled Reversible Anchoring of η6‐Arene/TsDPEN‐ Ruthenium(II) Complex onto Magnetic Nanoparticles: A New Strategy for Catalyst Separation and Recycling

A new catalyst separation and recycling protocol combining magnetic nanoparticles and host‐guest assembly was developed. The catalyst, (η⁶‐arene)[N‐(para‐toluenesulfonyl)‐1,2‐diphenylethylenediamine]ruthenium trifluoromethanesulfonate [Ru(OTf)(TsDPEN)(η⁶‐arene)] bearing a dialkylammonium salt tag, was easily separated from the reaction mixtures by magnet‐assisted decantation, on basis of the formation of a pseudorotaxane complex by using dibenzo[24]crown‐8‐modified Fe₃O₄ nanoparticles. The ruthenium catalyst has been successfully reused at least 5 times with the retention of enantioselectivity but at the expense of relatively low catalytic activities in the asymmetric hydrogenation of 2‐methylquinoline.     

Asymmetric Hydrogenation Catalyzed by (S,S)‐R‐BisPast;‐Rh and (R,R)‐R‐MiniPHOS Complexes: Scope,Limitations, and Mechanism

A new class of chiral C₂‐symmetric bis(trialkyl)phosphine ligands has been prepared and used in Rh(I)‐catalyzed asymmetric hydrogenation reactions. The ligands, 1,2‐bis(alkylmethylphosphino)ethanes 1a‐g (abbreviated as BisP*, alkyl = t‐butyl, 1‐adamantyl, 1‐methylcyclohexyl, 1,1‐diethylpropyl, cyclopentyl, cyclohexyl, isopropyl) and 1,2‐bis(alkylmethylphosphino)methanes 2a‐d (abbreviated as MiniPHOS, alkyl = t‐butyl, cyclohexyl, isopropyl, phenyl) are prepared by a simple synthetic approach based on the air‐stable phosphine–boranes. These new ligands give the corresponding Rh(I) complexes, which are effective catalytic precursors for the asymmetric hydrogenation of a representative series of dehydroamino acids and itaconic acid derivatives. Enantioselectivities observed in these hydrogenations are universally high and in many cases exceed 99%. X‐Ray characterization of four precatalysts, study of the pressure effects, deuteration experiments, and characterization of the wide series of intermediates in the catalytic cycle are used for the discussion of the possible correlation between the structure of the catalysts and the outcome of the catalytic asymmetric hydrogenation.     

Molecular Iodine‐Mediated Domino Reaction for the Synthesis of Benzamides, 2,2‐Diazidobenzofuran‐3(2H)‐ones and Benzoxazolones

A simple and efficient domino protocol has been developed for the preparation of biologically important benzamides, 2,2‐diazidobenzofuran‐3(2H)‐ones and benzoxazolones from various structurally and electronically divergent acetophenones and ortho‐hydroxyacetophenones in the presence of molecular iodine, sodium azide and sodium bicarbonate at 100 °C in good to excellent yields.

     

Potassium Iodide/tert‐Butyl Hydroperoxide‐Mediated Oxidative Annulation for the Selective Synthesis of N‐Substituted 1,2,3‐Benzotriazine‐4(3H)‐ones Using Nitromethane as the Nitrogen Synthon

A novel and efficient oxidative annulation of 2‐aminobenzamides with nitromethane has been developed for the chemoselective synthesis of N‐substituted 1,2,3‐benzotriazine‐4(3H)‐ones in moderate to excellent yields under transition metal‐free conditions. Two N N bonds were constructed in one pot via C N cleavage of nitromethane, which was selectively employed as the nitrogen synthon. The preliminary mechanistic studies revealed that this protocol proceeded under hypoiodite catalysis generated in situ.