Base-catalyzed condensation of β-bromovinylaldehydes with β-ketoesters followed by water-mediated cyclization and aromatization: one-pot access to substituted benzene derivatives

A simple, convenient, one-pot synthetic approach towards substituted benzene derivatives using base-catalyzed condensation of β-bromovinylaldehydes with β-ketoesters followed by water-mediated cyclization and aromatization has been developed.     

Reaction of α-halogen substituted β-ethoxyvinyl trifluoromethyl ketones with 2-aminopyridine: new route to trifluoroacetyl-containing heterocycles

The reaction of α-halosubstituted β-ethoxyvinyl trifluoromethyl ketones with 2-aminopyridine gives 3-trifluoroacetyl imidazo[1,2-a]pyridine and 3-halo-1,1,1-trifluoro-4-(2-pyridinylamino)-3-buten-2-ones. The product ratio depends on the nature of the α-halogen atom and the solvent.     

A new route to fullerene substituted phenylalanine derivatives

A series of fullerene substituted phenylalanine derivatives have been prepared by the condensation of 1,2-(4'-oxocyclohexano)fullerene with ester or Boc protected (4-amino)phenylalanine, H(2)NC(6)H(4)CH(2)CH(COR(1))(NHCOR(2))(where R(1) = OMe, R(2) = Me; R(1) = OH, R(2) = Me, O(t)Bu). Conversion of the imine to the corresponding amine is achieved by di-acid catalyzed hydroboration. Reaction of the N-Ac amino ester with BBr(3) led to the formation of the parent amino acid, while the Boc-protected derivative readily undergoes coupling with NH(2)-Gly-OEt. The reduction of the imine is not accompanied by hydroboration of the fullerene cage.     

Nucleophile-assisted Pt-catalyzed cyclization of enynones: an access to synthesis of highly substituted furans

A new and efficient Pt-catalyzed hydroxy- or alkoxy cyclization of 2-(1-alkynyl)-2-alkene-1-ones offers a general synthetic pathway to a wide range of highly substituted furans in good to excellent yields.     

Ruthenium-catalyzed annulation of aromatic ketones with internal alkynes: A reliable route to substituted naphthalene derivatives

We report herein the preparation of polysubstituted naphthalene derivatives by the ruthenium-catalyzed benzannulation reaction of aromatic ketones with internal alkynes. This method (1) forms two new carbon-carbon bonds in one single step, (2) accommodates a variety of functional groups, and (3) undergoes mild reaction conditions.     

A convenient access to substituted benzothiazole scaffolds via intramolecular cyclization of thioformanilides

A new and practical method has been developed for the synthesis of substituted benzothiazoles via the intramolecular cyclization of thioformanilides using DDQ in CH₂Cl₂ at ambient temperature. The reaction proceeds in high yields via the thiyl radical to give novel oxybis-benzothiazole, and offers a high degree of flexibility with regard to the functional groups that can be placed on the benzothiazole nucleus or 2-aryl moiety which in turn generates scaffolds for parallel synthesis.     

Cycloadditions of substituted benzopyran-4-ones to electron-rich dienes: a new route to xanthone derivatives

The benzopyranones 1 and 3 reacted with 2,3-dimethyl-1,3-butadiene in the presence of titanium (IV) chloride to give the corresponding (4 + 2) cycloadducts 8 and 11, the former undergoing facile deformylation to give 9 and 10. Compounds 1, 3, and 4 underwent efficient uncatalysed cycloaddition to 1- methoxy-3-(trimethylsilyloxy)-l,3-butadiene 12 to give the respective adducts 13,14, and 18 as mixtures of C-l stereoisomers. Heating the 3-arylsulphinylchromone 5 with the diene 12 afforded 3-hydroxyxanthone 23 in 50% yield, the presumed cycloaddition - elimination sequence constituting a new route to xanthone systems. Desilylation of 13,14, and 18 in acidic media provided 25,26, and 27 respectively.     

Synthesis of substituted carbazoles and β-carbolines by cyclization of diketoindole derivatives

A new route to substituted β-carbolines and carbazoles is described. Diketoindole intermediates, prepared by Friedel-Crafts acylations of 3-substituted indoles, have been converted to 3-hydroxycarbazoles and β-carbolines in good yields, 51-96% and 82-97%, respectively. This method also allows for the formation of 4-substituted β-carbolines. The application of this methodology to the synthesis of the natural products hyellazole and 6-chlorohyellazole is also described.     

Palladium-catalyzed cyclization reactions of propargylic carbonates with nucleophiles: a methodology for the syntheses of substituted 2,3-dihydrofurans and benzofurans

Phenoxy-substituted 2,3-dihydrofurans were synthesized by the palladium-catalyzed reaction of 5-methoxycarbonyloxy-3-pentyn-1-ol with phenols. The propargylic carbonate containing a nucleophilic phenoxy group also reacted in the presence of palladium to produce the product. The reaction of 1-(2-hydroxyphenyl)-3-methoxycarbonyloxy-1-propyne with 2-methyl-1,3-cyclohexanedione or 2-methyl-1,3-cycohexanedione yielded the substituted benzofurans. The propargylic compound having a acetoxy group as a leaving group exhibited similar reactivity.     

A tandem radical cyclization route to tricyclo[4.3.n.0]alkanes

A facile route to tricyclo[4.3.n.0^1,5]alkane skeletons from conjugated cyclic enones was developed through tandem free radical cyclization reaction sequence involving the cyclopropylmethyl radical mediated rearrangement. The scope and limitation of the reaction was investigated.     

Base induced cyclization of some quinolines. Formation of fused nitrogen heterocyclic ring system

Condensation of 3,5-dinitro-4-chloro-6-methoxy-2-methylquinoline (1) with benzylamine, ethanolamine and/or thioglycolic acid afforded the quinoline derivatives4 a-c. Cyclization of4 a and4 b with alkali and condensation of1 with glycine in sodium carbonate solution furnish 2H-imidazo[4,5-c]quinoline derivatives5 a-c, respectively. Treatment of5 b with benzaldehyde in presence of zinc chloride gave the styryl derivative6. 1 reacted with sodium azide to give the azido derivative4 d, which upon treatment with phenylhydrazine or sodium borohydride yielded the 4-amino derivative4 3. Moreover,1 was treated with phenylhydrazine to give4 f, which cyclized in 10% sodium hydroxide solution to the corresponding v-triazolo[4,5-c]quinoline 3-oxide derivative7. When however4 f was treated with dilute hydrochloric acid, the corresponding phenylpyrazolo[3,4,5-de]quinoline derivative8 was obtained.

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Baseninduzierte Cyclisierung einiger Chinoline. Darstellung höherer Stickstoff-Heterocyclen

Zusammenfassung Kondensation von 3,5-Dinitro-4-chlor-6-methoxy-2-methylchinolin (1) mit Benzylamin, Ethanolamin und/oder Thioglycolsäure ergab die Chinolinderivate4 a-c. Cyclisierung von4 a und4 b mit Alkali und Kondensation von1 mit Glycin in Natriumcarbonatlösung lieferte 2H-imidazo[4,5-c]chinolin-Derivate5 a-c. Behandlung von5 b mit Benzaldehyd in Gegenwart von Zinkchlorid ergab das Styrylderivat6. 1 wurde mit Natriumazid zum Azidoderivat4 d umgesetzt, das mit Phenylhydrazin oder Natriumborhydrid zum 4-Aminoderivat4 e weiterreagierte.1 ergab mit Phenylhydrazin4 f, das in 10% NaOH-Lösung zum entsprechenden Triazolo[4,5-c]chinolin-Derivat7 cyclisierte. Aus4 f wurde mit verdünnter Salzsäure das Phenylpyrazolo[3,4,5-de]chinolin8 erhalten.

     

A new and effective route to (±)-botryodiplodin and (±)-epi-botryodiplodin acetates using a halogen atom transfer Ueno-Stork cyclization

(±)-Botryodiplodin and (±)-epi-botryodiplodin acetates were prepared in good yields following a practical four step route. The method, for the construction of the strategic tetrahydrofuran ring, hinged on an unprecedented halogen atom transfer Ueno-Stork cyclization of an O-allyl α,α-dihalohemiacetal acetate, catalyzed by the redox complex CuCl/N,N,N′,N″,N″-pentamethyldiethylenetriamine.     

Unique ionic iodine atom transfer cyclization: a new route to iodomethylated pyrrolidine derivatives from gamma-iodoolefin and chloramine-T

[reaction: see text] Pyrrolidines and bicyclic pyrrolidine derivatives can effectively be synthesized from gamma-iodoolefins using commercially available chloramine-T (CT) as a nitrogen source. The cyclization proceeds with high stereoselectivity via a cyclic iodonium intermediate.     

Synthesis and structure of new 1,3,5-triazine-pyrazole derivatives

We have studied the reaction of methylenedicarbonyl compounds with 4,6-disubstituted 2-hydrazinyl-1,3,5-triazine in order to obtain novel coupled biheterocyclic aromatic systems with potential bioactivity. Reaction conditions were studied and optimized, and a series of 4,6-disubstituted 2-(1H-pyrazolyl)-1,3,5-triazines were obtained with good yield.     

oxidative cyclization of α-(o-iodophenyl)cinnamic acids as a new route to certain phenanthrene derivatives

Conclusions The cyclization of the-(o-iodophenyl)-m- and-(o-iodophenyl)-p-bromocinnamic acids using K₂S₂O₈ in conc. H₂SO₄ gave the 2-bromo- and 3-bromo-10-carboxydibenz[b,f]iodepinium betaines, whose thermolysis in conc. HI leads to the 2-bromo- and 3-bromo-9-phenanthrenecarboxylic acids. The analogous cyclization does not go in the case of the-(o-iodophenyl)-p- and-(o-iodophenyl)-o-nitrocinnamic acids.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2530–2534, November, 1980.     

Convenient one-pot MCRs to trifluoromethylated spiropiperidine under catalyst-free conditions

One-pot, four-component reactions of 1,2-diphenylpyrazolidine-3,5-dione, ethyl 4,4,4-trifluoroacetoacetate, aromatic aldehyde and ammonium acetate afforded highly functionalized ethyl 8-hydroxy-1,4-dioxo-2,3,6,10-tetraphenyl-8-(trifluoromethyl)-2,3,7-triazaspiro[4.5]decane-9-carboxylate derivatives 5 in good yields. The most advantage of this reaction was the high diastereoselectivity because only one diastereoisomer 5 was produced. The effect of NH₄OAc and solvents on the reaction efficiency and yield was briefly investigated. Meanwhile, the further transformation of hemi-aminal moieties to the corresponding dehydrated product was also achieved under the mild reaction conditions. And a plausible reaction mechanism for the formation of products 5 was illustrated based on the control experiments.     

Organocatalytic multicomponent alpha-methylenation/Diels-Alder reactions: a versatile route to substituted cyclohexenecarbaldehyde derivatives

This article describes the design and optimization of an effective organocatalytic three-component domino alpha-methylenation/Diels-Alder reaction to produce vinyl-substituted cyclohexenecarboxaldehydes in a highly regioselective fashion. In these one-pot transformations, 2-formyl-1,3-butadienes (4) were prepared in situ from alpha,beta-unsaturated aldehydes and formalin and were subsequently trapped with a variety of buta-1,3-dienes. The outcomes of the reactions were dependent on the electronic properties of the dienes. 1-Vinylcyclohexenecarbaldehydes 6 were formed by use of acyclic electron-rich dienes, while the initially formed cycloadducts of 4 with cyclopentadiene underwent Cope rearrangements, leading to the formation of tetrahydro-3H-indene-5-carbaldehyde compounds 7. The mechanisms involved in these reactions were deduced from experimental findings. Furthermore, the method was also extended to one-pot domino methylenation/Diels-Alder reactions of dihydrofurans and dihydropyrans to yield spirocyclic lactols 22. In these reactions, the unstable intermediate hydroxyethyl and hydroxypropyl acroleins behaved as dienophiles, undergoing cycloaddition reactions with dienes with good yields and selectivities. The wide variety of functionalized 1-vinylcyclohex-3-enecarbaldehydes 6, 4-vinylcyclohex-1-enecarbaldehydes 7, and spiro lactols 22 generated through the use of these organocatalytic domino processes as a diversity-oriented synthesis provided useful intermediates for the construction of novel odorants.     

Mild and efficient cyclization reaction of 2-ethynylaniline derivatives to indoles in aqueous medium

Results of the optimized cyclization reaction of 2-ethynylaniline derivatives to indoles catalyzed by copper(II) salts are described. The reactions can be carried out in a mixture of H₂O and MeOH in the presence of 1-ethylpiperidine at room temperature. These conditions can be applied to a bulky substrate, which is difficult to be cyclized efficiently by existing reaction conditions. Furthermore, this reaction condition was applied to a catalyst recycling reaction system.     

The intramolecular sila-Pummerer cyclization: A new route to sulfur heterocycles

The generality of the intramolecular cyclization of suitable nucleophilic sites to a  S⁺CH₂ center created by a sila-Pummerer rearrangement has been investigated. Successful nucleophilic sites included the OH group (in alcohols, carboxylic acids, and hydroxylamines) and the NH group (in amines and carbamates): attempts to produce carbon-based nucleophilic sites were not effective. Successful cyclizations were achieved to produce sulfur heterocycles with 5-, 6-, and 7-membered rings.