Synthesis of fully substituted polyhydroxylated pyrrolizidines via Cope-House cyclization

Total synthesis of the proposed structure of (-)-hyacinthacine C(5) and its epimers at C6 and C7 is described. A key step of the synthesis was the construction of the bicyclic pyrrolizidine system by means of a nucleophilic addition of a dithiane to a cyclic nitrone followed by a Cope-House cyclization.     

Oxidative cyclization of thiophenolic and phenolic Schiff's bases promoted by PCC: a new oxidant for 2-substituted benzothiazoles and benzoxazoles

Pyridinium chlorochromate (PCC) supported on silica gel effects the oxidative cyclization of structurally diverse thiophenolic and phenolic Schiff's bases, thereby providing an efficient and convenient method for the synthesis of a library of 2-arylbenzothiazoles and 2-arylbenzoxazoles.     

Synthesis of benzofurans via Pd-catalyzed oxidative cyclization of 2-allylphenols

Substituted 2-methylbenzofurans were obtained from 2-allylphenols via Pd²⁺-catalyzed oxidative cyclization using Cu(OAc)₂–LiCl as a reoxidant and wet DMF as a solvent.     

Synthesis of 2,5-disubstituted 6-azaindoles from substituted aziridines via intramolecular cyclization

A new and efficient preparation of pharmacologically and biologically important 2,5-disubstituted 6-azaindoles was achieved from cyclizations of aziridin-2-yl dipropargylic alcohols as adducts of two propargyl groups to ethyl 1-benzylaziridine-2-carboxylate. The sequential cyclizations include pyrrole formation and a novel base-catalyzed intramolecular acetylenic Schmidt reaction.     

Cu-Nanoparticles: efficient catalysts for the oxidative cyclization of Schiffs’ bases

Cu-Nanoparticles provide an efficient catalysis for the synthesis of 2-arylbenzoxazoles by the coupling of aromatic or heteroaromatic aldehydes with 2-aminophenol though the oxidative cyclization of the Schiffs’ bases using 10 mol % of the Cu-nanoparticles in the presence of K₂CO₃ in MeOH. This method avoids the use of metal oxide or organic oxidizing agents, namely, DDQ or strong acids such as polyphosphoric acid or boric acid.     

Synthesis of 2‐(2‐, 3‐, and 4‐pyridyl)benzoxazoles by the reaction of phenolic schiff bases with thianthrene cation radical

2‐(2‐, 3‐, and 4‐Pyridyl)benzoxazole derivatives were prepared in excellent yields by the oxidative cyclization of phenolic Schiff bases with thianthrene cation radical perchlorate in the presence of 2,6‐di‐tert‐butyl‐4‐methylpyridine.     

Tin(II) chloride‐mediated synthesis of 2‐substituted benzoxazoles

2‐Aminophenols react with an array of carboxylic acids in dioxane at 180° in the presence of tin(II) chloride to afford the corresponding 2‐substituted benzoxazoles in good yields. The reaction is applicable to a wide range of alkyl, alkenyl, aryl carboxylic acids.     

Novel propargyl‐substituted azo‐coupled phenolic resins

Novel propargyl that contains phenolic resins via azo‐coupling reaction was synthesized. Peculiarities of curing process were investigated by differential scanning calorimetry analysis. Polymerization of resins with azo groups was estimated to be affected by radicals obtained at resin decomposition causing 10°C peak shift to lower temperatures in comparison with resin containing only propargyl group. At the same time, polymerization of triple propargyl bond was shown to not proceed at radical initiation until Cleisen rearrangement and chromene formation. Thermogravimetric analysis revealed increase of thermal stability by 170–190°C and char yield by up to 20% for modified resins in comparison with original novolac resin. Heat deflection temperature estimated by dynamic mechanical analysis was also shown to be increased by at least 110°C for modified resins in comparison with novolac resin. All the synthesized resins are soluble in acetone and used for preparation of unidirectional glass fiber‐based composites. Flexural strength and modulus for modified resins‐based composites were shown to increase by at least 25% and 10% correspondingly in comparison with novolac‐based composite. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis of novel benzo‐substituted macrocyclic schiff bases containing two triazole rings

A synthesis of a series of novel macrocyclic Schiff bases containing two triazole rings 10a,b, 11a,b, 34‐37 in good yields by heating the appropriate bis‐amines 1f, 6a,b, 31 with the corresponding bis‐aldehydes 2, 9a,b, 29 in refluxing acetic acid under high dilution conditions was described. Attempts to synthesize macrocyclic Schiff bases containing pyridine and two triazole rings were also described.     

Synthesis of substituted quinolines via B(C6F5)3‐catalyzed aniline‐aldehyde‐pyruvate oxidative annulation

A metal‐free method to construct quinoline derivatives via B(C₆F₅)₃‐catalyzed cyclization of anilines with aldehyde derivatives and pyruvates is described. This three‐component cascade reaction provides an efficient approach for the easy access to various substituted quinoline‐4‐carboxylic esters with 71% to 92% yield. The utility of this methodology was further demonstrated by gram‐scale formal synthesis of the antimalarial drug DDD107498.     

Synthesis of highly substituted pyrrolidines via palladium-catalyzed cyclization of 5-vinyloxazolidinones and activated alkenes

N-Tosyl-5,5-divinyloxazolidin-2-one undergoes a palladium-catalyzed decarboxylative cyclization across a range of electrophilic alkenes to give the corresponding pyrrolidine derivatives bearing two contiguous quaternary centres. Alkenes bearing two electron-withdrawing groups are required; pyrrolidines were not formed from mono-activated alkenes. Bulky, electron-rich phosphines promote pyrrolidine formation with less highly electrophilic, doubly activated alkenes, and a dramatic improvement is observed in the presence of iodide.     

Synthesis of alicyclic N‐substituted 1,3‐amino alcohols via 1,3‐oxazines

Alicyclic N‐substituted 1,3‐amino alcohols 13‐18 were prepared in a facile way in a one‐pot procedure from 1,3‐oxazines 5‐8 in the presence of a ketone 9‐12 . The complex reaction involves palladium‐catalyzed reduction, debenzylation and/or transimination and further reduction.     

Transformations of schiff bases derived from quinoline‐8‐carbaldehyde. Synthesis of C‐8 substituted quinolines

The Schiff bases derived from quinoline‐8‐carbaldehyde and substituted aromatic amines were used in the synthesis of C‐8 substituted quinolines. 3‐Aryl‐2‐(8‐quinolinyl)‐4‐thiazolidinones were prepared from obtained aldimines by means of the cyclocondensation of mercapto acids. A series of 4‐N‐arylamino‐4‐(8‐quinolinyl)‐1‐butenes was synthesized through the addition of the Grignard reagent (allylmagnesium bromide) to the double bond C=N of these aldimines. The structure of the prepared compounds was established on the basis of their elemental analyses and spectral data.     

Synthesis of unsymmetrical arylthiophenes and bithienyls via oxidative cyclization of 1,3-butadiene-1-thiols

Oxidative cyclization of 2-mercapto-5-aryl-2,4-pentadienoic acids with iodine produced the respective 5-aryl-2-thenoic acids. The method was also suitable for the synthesis of unsymmetrical substituted 2,2′-bithienyls, and 2,3′-bithienyls. The synthesis of 5-carboxy-2′-bromo-5′-phenyl-2,3′-bithienyl from benzal-acetone demonstrated that oxidative cyclization of 1,3-butadiene-1-thiols is a useful procedure for preparing 5′-aryl-2,3′-bithienyls from simple carbonyl compounds. Preferential ring bromination of 2-phenyl-4-methyl-thiophene with N-bromosuccinimide and a radical catalyst was also observed.     

Direct synthesis of γ‐substituted phthalides via ortho‐aryl benzoic acid mediated benzyl radical cyclization

Direct synthesis of γ‐substituted phthalids from related ortho‐aryl benzoic acids with 48–85% yield are covered. The direct oxidation in the presence of peroxydisulphate‐copper (II) chloride in aqueous medium was applied. The reaction is highly regioselective and leads exclusively to γ‐butyrolactone, through very stable benzylic radical intermediate.     

Synthesis of pyrethroids via epxoyamide cyclization

LDA-induced cyclization of $\text{4}$ yields $\text{5}$, the $\text{trans}$-isomer of which undergoes dehydration using Ph₂S[OC(CF₃)₂Ph]₂ to give the pyrethroid amide $\text{6}$.     

Synthesis of 2,4,6‐trisubstituted naphthalenes via novel copper‐promoted tandem coupling and intramolecular cyclization

An unprecedented copper‐promoted tandem coupling and intramolecular cyclization reaction is disclosed. This strategy offers a simple and promising method for accessing 2,4,6‐trisubstituted naphthalenes. A reaction mechanism involving initial formation of diynes followed by a 6‐exo‐dig cyclization and subsequent rearrangement is proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of isoxazoles via electrophilic cyclization

[reaction: see text] A variety of 3,5-disubstituted 4-halo(seleno)isoxazoles are readily prepared in good to excellent yields under mild reaction conditions by the reaction of 2-alkyn-1-one O-methyl oximes with ICl, I2, Br2, or PhSeBr.