Highly Regio‐ and Stereoselective Iodohydroxylation of 1,2‐Allenylic Sulfoxides in the Presence of Benzyl Thiol

The iodohydroxylation of 1,2‐allenyl sulfoxides with iodine in the presence of benzyl thiol afforded 3‐hydroxy‐2‐iodo‐2(E)‐alkenyl sulfides in good yields and high regio‐ and stereoselectivities. In this reaction it was observed that the sulfoxide functionality was reduced to sulfide and the water in the reaction mixture plays an important role for the stereoselectivity observed. A mechanism involving the attack of benzyl thiol at the positively charged sulfur atom in the five‐membered intermediate 2 has been proposed.     

Studies on Electrophilic Interaction of 2,3‐Allenols with Electrophilic Halogen Reagents: Selective Synthesis of 2,5‐Dihydrofurans, 3‐Halo‐3‐alkenals,or 2‐Halo‐2‐alkenyl Ketones

The reaction of primary 2,3‐allenols with iodine (I₂) afforded 2,5‐dihydrofurans while that of readily available 1‐aryl or 1‐methyl substituted 2,3‐allenols with bromine (Br₂), N‐bromosuccinimide (NBS), I₂ or N‐iodosuccinimide (NIS) formed the not easily available but synthetically useful 3‐halo‐3‐alkenals and 2‐halo‐2‐alkenyl ketones with good selectivity and yields via a sequential electrophilic interaction of X⁺ with the allene moiety, 1,2‐aryl or 1,2‐proton shift, and H⁺ elimination process.     

Highly Regio‐ and Diastereoselective Palladium‐Catalyzed Allylic Substitution. Synthesis of 3‐(2‐Aminobutylidene)‐ 4‐arylazetidin‐2‐ones

The palladium‐catalyzed benzylamine attack to a particular allylic moiety, the 3‐alkenyl‐3‐bromoazetidin‐2‐one is herein reported. This reaction shows interesting mechanistic aspects and allows us to introduce in one step and under high regio‐ and stereocontrol the amino function in the C3 side chain of non‐conventional β‐lactams, thus offering the opportunity for designing new potential glutamine syntethase inhibitors, such as Tabtoxin analogues.     

Iron‐Catalyzed Synthesis of Allenes from 2‐Alken‐4‐ynoates and Grignard Reagents

Treatment of 2‐alken‐4‐ynoates with methyl‐ or aryl‐Grignard reagents and iron(II) chloride (10 mol%) afforded 5‐methyl‐ or 5‐aryl‐3,4‐alkadienoates in good yields as a single isomer after aqueous work‐up. Likewise, (2‐alken‐4‐ynoyl)oxazolidinones afforded (5‐methyl‐3,4‐alkadienoyl)oxazolidinones. The aldol‐type reaction with acetone was also possible in place of the hydrolytic work‐up.     

Synthesis of 3‐(2‐Nitroalkyl)pyrroles from Sulfonylpyrroles and their Conversion to 6‐Azaindole Derivatives

The reaction of sulfonylpyrroles with nitroalkanes in the presence of KF/alumina generates 3‐(2‐nitroalkyl)pyrroles in good yields. These compounds can be converted into trisubstituted 6‐azaindoles by a sequence of reactions comprising reduction of the nitro group, Pictet–Spengler cyclization and final oxidative aromatization.

     

Copper‐Catalyzed Chloroamination of Alkynes: Highly Regio‐ and Stereoselective Synthesis of (E)‐β‐Chloro‐Enesulfonamides

An efficient copper catalysis system for the chloroamination of alkynes with chlorosulfonamide at room temperature is described, providing a highly regio‐ and stereoselective procedure for the synthesis of (E)‐β‐chloro‐enesulfonamides in moderate to good yields.     

Regioselective Addition of Organometallic Reagents to 2‐(1‐Alkynyl)‐2‐alken‐1‐ones for an Efficient Synthesis of Substituted 1,2‐Allenyl Ketones

Highly substituted 1,2‐allenyl ketones can be easily and efficiently prepared from organometallic reagents and readily available 2‐(1‐alkynyl)‐2‐alken‐1‐ones. The synthetic application of 1,2‐allenyl ketone products was also showcased by palladium‐catalyzed further transformation.     

Synthesis of Chiral 2‐Hydroxy‐1‐methylpropanoates by Rhodium‐Catalyzed Stereoselective Hydrogenation of α‐(Hydroxymethyl)‐acrylate Derivatives

The synthesis of chiral 3‐hydroxy‐2‐methylpropanoic acid esters (e.g., “Roche ester” 3a ) based on the rhodium‐catalyzed stereoselective hydrogenation of Baylis–Hillman reaction products was investigated. Full conversions and enantioselectivities of up to 99% at a substrate/catalyst ratio of up to 500/1 were achieved by application of bisphospholanes of the catASium M series as ancillary ligands. An interesting kinetic resolution was observed by the diastereoselective hydroxy‐directed hydrogenation of related racemic β‐branched precursors affording mainly anti‐isomers with up to 96%ee.     

Copper‐Catalyzed Trifluoromethylation of Acrylamides Coupled with Indole Dearomatization: Access to Trifluoromethyl‐Substituted Spiro[indole‐3,3′‐pyrrolidine] Derivatives

A copper‐catalyzed cascade reaction involving trifluoromethylation of acrylamides coupled with ring closure and indole dearomatization is reported. This facile transformation was highly regioselective and proceeded under mild conditions, allowing efficient access to trifluoromethyl‐substituted spiro[indole‐3,3′‐pyrrolidine] derivatives, which are of increasing interest to the pharmaceutical industry.

     

Synthesis and characterization of the soluble fluorescent poly[2‐decyloxy‐5‐(2′‐(6′‐dodecyloxy)naphthyl)‐1,4‐phenylenevinylene]

A new soluble fluorescent polymer, poly[2‐decyloxy‐5‐(2′‐(6′‐dodecyl‐oxy)naphthyl)‐1,4‐phenylenevinylene] (DDN‐PPV), with no tolane‐bisbenzyl (TBB) structure defects is prepared by the dehydrohalogenation of 1,4‐bis(bromomethyl)‐2‐decyloxy‐5‐(2′‐(6′‐dodecyloxy)naphthyl)benzene (as monomer) in this study. The aforementioned monomer is synthesized via such chemical reactions as alkylation, bromination, and Suzuki coupling reactions. The structure and properties of the DDN‐PPV are examined by ¹H NMR, FTIR, UV/vis, TGA, photoluminescence (PL), and electroluminescence (EL) analyses. The two asymmetric decyloxy and 6′‐dodecyloxynaphthyl substituents on the phenylene ring make the DDN‐PPV soluble in organic solvents and eliminate the TBB structure defects. With the DDN‐PPV acting as a light‐emitting polymer, a device is fabricated with a sequential lamination of ITO/PEDOT/DDN‐PPV/Ca/Ag. The EL spectrum of the device shows a maximum emission at 538 nm. The turn on voltage of the device is about 16.6 V. Its maximum brightness is 14 cd/m² at a voltage of 18.2 V. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2734–2741, 2007     

Copper‐Catalyzed Monoborylation of Silylalkynes; Regio‐ and Stereoselective Synthesis of (Z)‐β‐(Borylvinyl)silanes

The selective copper‐catalyzed borylation of silylalkynes in the presence of a diboron reagent and methanol produced a variety of (Z)‐β‐(borylvinyl)silanes. The appropriate use of a selective ligand for copper allows the chemo‐, regio‐, and stereoselective monoborylation of silylalkynes. The β‐regioselectivity of an N‐heterocyclic carbene (NHC)‐copper catalyst was investigated by DFT calculations.

     

Silver‐Catalyzed Intramolecular Cyclization of o‐(1‐Alkynyl)benzamides: Efficient Synthesis of (1H)‐Isochromen‐1‐imines

An efficient avenue for the facile and atom‐economic synthesis of (1H)‐isochromen‐1‐imines has been developed, and a broad spectrum of substrates can participate in the process effectively to produce the desired products in good yields. Significantly, this is the first report of the synthesis of (1H)‐isochromen‐1‐imines that involves a silver(I)‐catalyzed, regiocontrolled intramolecular addition of the carbonyl group of the amide moiety towards an alkyne.     

Gold(I)‐Catalyzed Reactions of 1‐(ortho‐Alkynylaryl)ureas: Highly Selective Heterocyclization and Synthesis of Mixed N,O‐Acetals

Readily available 1‐(ortho‐ethynylaryl)urea derivatives undergo a selective gold/silver {[AuCl(IPr)]/AgSbF₆} catalyzed N‐6‐exo‐dig or N‐5‐endo‐dig heterocyclization process in dimethylformamide (DMF) at 60 °C. Benzoxazine derivatives, i.e., the products of O‐6‐exo‐dig ring closure through the urea oxygen, could be observed under catalytic conditions only when the N‐3 basicity was substantially diminished, but were readily isolable in stoichiometric processes carried out at low temperature. The open chain amino O,O‐acetals and a series of new cyclic mixed N,O‐acetals containing the trifluoroethyl group were synthesized when the reactions were performed in ethanol or trifluoroethanol, respectively, as solvent. The procedure allows for an easy access to this versatile class of key intermediates in organic synthesis from simple starting materials. The effect of using either DMF or protic solvents on the course of the reactions is reported.

     

Asymmetric α‐Hydroxylation of β‐Indanone Esters and β‐Indanone Amides Catalyzed by C‐2′ Substituted Cinchona Alkaloid Derivatives

The highly catalytic asymmetric α‐hydroxylation of β‐indanone esters and β‐indanone amides using peroxide as the oxidant was realized with a new C‐2′ substituted Cinchona alkaloid derivatives. The two enantiomers of α‐hydroxy‐β‐indanone esters could be obtained by simply changing the oxidant. This protocol allows a convenient access to the corresponding α‐hydroxy‐β‐indanone esters and α‐hydroxy‐β‐indanone amides with up to 99% yield and 98% ee.

     

Efficient Catalytic Asymmetric Synthesis of trans‐5‐Aryl‐2‐substituted Cyclohexanones by Rhodium‐Catalyzed Conjugate Arylation of Racemic 6‐Substituted Cyclohexenones

Catalytic asymmetric conjugate arylation of racemic 6‐substituted cyclohexenones with arylboronic acids was catalyzed by 3 mol % of chiral amidophosphane‐[RhCl(C₂H₄)]₂ in a 10:1 mixture of 1,4‐dioxane and water at 70 °C to afford a nearly 1:1 mixture of trans‐ and cis‐5‐aryl‐2‐substituted cyclohexanones in high enantioselectivity, which was subsequently epimerized with sodium ethoxide in ethanol to give thermodynamically stable trans‐5‐aryl‐2‐substituted cyclohexanones with 99–97 % ee in high two‐step yields.     

Synthesis and Properties of Branched Oligo(2‐thienyl)‐ and Oligo(2,2′‐bithien‐5‐yl)‐Substituted Pyridine Derivatives

Starting from easily accessible precursors we describe the preparation of a series of branched oligo(2‐thienyl)‐ and oligo(2,2′‐bithienyl)‐substituted pyridine derivatives. With palladium‐catalyzed cross‐coupling reactions of pyridyl nonaflates/triflates as key steps we synthesized 2,6‐di(2‐thienyl)pyridines bridged by thiophene or benzene rings. By selective bromination of 2,6‐di(2‐thienyl)pyridine and 2,4,6‐tri(2‐thienyl)pyridine and subsequent coupling reactions an access to oligo(2,2′‐bithien‐5‐yl)‐substituted pyridine derivatives was gained. The constitution and solid state conformation of 2,6‐bis(2,2’‐bithien‐5‐yl)pyridine was determined by X‐ray analysis. This series of new pyridine‐thiophene conjugates was systematically investigated by UV/vis spectroscopy. Large Stokes shifts in the neutral and protonated form were observed. The electrochemical oxidation of two typical compounds was studied, however, these oxidations were irreversible forming a polymeric film at the anode. As a selected example, a thiophene‐bridged 2,6‐di(2‐thienyl)pyridine derivative was also investigated by scanning tunneling microscopy showing an interesting self‐assembly into a highly ordered monolayer on highly oriented pyrolytic graphite.

     

Gold(I)‐Catalyzed Regio‐ and Stereoselective 1,3‐Dipolar Cycloaddition Reactions of 1‐(1‐Alkynyl)cyclopropyl Oximes with Nitrones: A Modular Entry to Highly Substituted Pyrrolo[3,4‐d][1,2]oxazepines

An efficient approach for the synthesis of highly substituted pyrrolo[3,4‐d][1,2]oxazepines has been achieved by gold(I)‐catalyzed 1,3‐dipolar cycloaddition reactions of 1‐(1‐alkynyl)cyclopropyl oximes with nitrones in good to excellent yields as a single diastereomer. A complete chirality transfer was observed in this transformation.     

3‐Hydroxy‐2‐[1′‐phenyl‐3′‐(p‐chlorophenyl)‐4′‐pyrazolyl]‐4‐oxo‐4H‐1‐benzopyran as a spectrophotometric reagent for trace determination of tungsten(vi)

3‐Hydroxy‐2‐[1′‐phenyl‐3′‐(p‐chlorophenyl)‐4′‐pyrazolyl]‐4‐oxo‐4H‐1‐benzopyran solution in acetone forms a yellow‐coloured complex with tungsten(vi ) in perchloric acid medium which is extractable into chloroform after equilibration. In this study, tests were carried out on this compound and it was found to be quite stable and to obey Beer’s law. Interactions with various ions were studied and the molar absorptivity, Sandell’s sensitivity and relative standard deviation were also investigated. Job’s method, the mole ratio method and the equilibrium‐shift method were also used. The ratio of metal to ligand was measured using a method that was simpler, more accurate, sensitive, rapid and selective as compared with existing methods. This method is applicable to the analysis of various samples of varied composition.     

Highly Enantioselective Michael Addition Reactions of 3‐Substituted Benzofuran‐2(3H)‐ones to Chalcones Catalyzed by a Chiral Alkyl‐Substituted Thiourea

A highly enantioselective Michael addition of 3‐substituted benzofuran‐2(3H)‐ones to chalcones catalyzed by a chiral bifunctional thiourea was developed. Several chiral 3,3′‐substituted benzofuran‐2(3H)‐ones derivatives, bearing adjacent quaternary‐tertiary stereocenters, were efficiently synthesized with excellent enantioselectivities.     

Efficient Method for the Synthesis of Optically Active 2‐Amino‐2‐chromene Derivatives via One‐Pot Tandem Reactions

The asymmetric synthesis of functionalized 2‐amino‐2‐chromene derivatives with high enantioselectivities via one‐pot tandem reactions of functionalized α,β‐unsaturated ketones with malononitrile catalyzed by 9‐amino‐9‐deoxyepiquinine ( 1a ) in combination with (R)‐1,1′‐binaphth‐2,2′‐diyl hydrogen phosphate ( 1c ) is reported for the first time.