Palladium-catalyzed intramolecular carbopalladation/cyclization cascade: access to polycyclic N-fused heterocycles

An efficient palladium-catalyzed intramolecular carbopalladation/cyclization cascade toward tetra- and pentacyclic N-fused heterocycles has been developed. This transformation proceeds via the palladium-catalyzed coupling of aryl halides with internal propargylic esters or ethers followed by the 5-endo-dig cyclization leading to polycyclic pyrroloheterocycles in moderate to excellent yields.     

Thiol-mediated radical cyclization: regioselective formation of indole-annulated sulfur heterocycles by tandem cyclization

Indole-2-yl-prop-2-ynyl sulfides, under thiophenol-mediated alkenyl radical cyclization conditions, afforded exclusively 4-thiophenyl-2,3,4,9-tetrahydrothiopyrano[2,3-b]indoles or 3-thiophenylmethyl-2,3,8-trihydrothieno[2,3-b]indoles depending on the substituent at the indole nitrogen.     

Lewis acid-induced intramolecular Friedel-Crafts cyclization of 1,3-bis-exocyclic dienes. a new route to 4a-methyltetrahydrofluorenes

[reaction: see text] An efficient new method for constructing the 4a-methyltetrahydrofluorene skeleton was achieved via Friedel-Crafts intramolecular cyclization of 1,3-bis-exocyclic dienes. This strategy offers a simple and promising method for accessing complex structures.     

Regioselective synthesis of quinolone-annulated sulfur heterocycles by aryl radical cyclization

The tin hydride-mediated cyclizations of a number of sulfides and sulfones under mild, neutral conditions, have been investigated accompanied by some amount of β-scission product for sulfides. The sulfides were derived from 4-mercaptoquinolone and 2-bromobenzyl bromides by phase transfer catalyzed reaction and the corresponding sulfones were prepared by treatment of the sulfides with m-CPBA at room temperature. The sulfides and the corresponding sulfones were then reacted with ⁿBu₃SnH-AIBN to give regioselective quinolone-annulated sulfur heterocycles.     

Novel intramolecular cyclization of N-alkynyl heterocycles containing proximate nucleophiles

Intramolecular cyclization of 2-acyl-1-propargyl-1H-indoles in the presence of ammonia provides an easy entry to pyrazino[1,2-a]indole nucleus.     

A new strategy to sulfur heterocycles: Reactions of an allene episulfide with electrophiles

A variety of sulfur-containing five- and six-membered cyclic compounds was obtained by the acid-catalyzed and thermal reactions of an allene episulfide with various electrophiles.     

Free radical intramolecular cyclization in the synthesis of heterocycles (review)

The possibilities of homolytic cyclization for the synthesis of heterocyclic compounds are examined. Factors affecting the yield and structure of the resulting products are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1011–1034, August, 1993.     

Solid-phase parallel synthesis of natural product-like diaza-bridged heterocycles through Pictet-Spengler intramolecular cyclization

A multistep, practical solid-phase strategy for the synthesis of natural product-like diaza-bridged heterocycles was developed. A key step in the library synthesis is tandem acidolytic cleavage with subsequent in situ iminium formation followed by the Pictet-Spengler intramolecular cyclization. The Pictet-Spengler-type intramolecular cyclization step was regioselective and diastereoselective to give final products as single diastereomers in exceptional yields and purities, which was confirmed by NMR structural study and LC/MS analysis. This approach is exemplified by the preparation of a 384-member library of 3,9-diazabicyclo[3.3.1]non-6-en-2-one skeletons, fused with indole and dihydroxybenzene and diversified at two bridging nitrogen atoms, using the solid-phase parallel synthetic methodology without further purification. In this pilot library, two diastereomerically enriched diaza-bridged core skeletons were modified by amide and urea bond formation on bridging nitrogen atoms, and this scheme exhibits the potential for expansion to obtain further diversification.     

A palladium-catalyzed approach to polycyclic sulfur heterocycles

The synthesis of a variety of polycyclic thiophenes and benzothiophenes is accomplished via a palladium-catalyzed domino ortho-alkylation/direct arylation reaction. An examination of the intramolecular direct arylation of thiophenes suggests that an electrophilic metalation mechanism may be present. This method was further extended to include the synthesis of a (thieno)benzoxepine.     

Laser photochemistry: The intramolecular cyclization of carvone to carvonecamphor

Kr-ion laser irradiation of carvone ($\text{1}$) at 350.7 and 356.4 nm gave carvonecamphor ($\text{2}$) in a much higher yield (88%) than in conventional photochemistry, while ($\text{3}$) was a primary photo-by-product.     

A radical cyclization route to cyclic imines

A novel route to cyclic imines based on 5-exo radical cyclization is explored. The radical precursors are imines prepared from allylamine and readily available α-phenylselenenyl ketones.     

A new tetradentate nitrogen ligand for organometallic catalysis: electrochemical nickel-catalyzed intramolecular cyclization

The new tetraaza-molecule, 1 has been synthesized and used as a ligand for a cationic mononuclear nickel(II) complex. This complex is an efficient catalysts for the intramolecular electrochemical cyclization of o-haloaryl compounds containing unsaturated side chains.     

Base-catalyzed cyclization of monofluorodienynes: a new route to substituted fluorobenzene derivatives

The Sonogashira reaction of 1-bromo-1-fluoro-4-phenyl-1,3-butadienes and terminal alkynes, followed by cyclization in the presence of DABCO in refluxing NMP affords fluorinated benzene derivatives site-specifically in good yields.     

Unexpected intramolecular nucleophilic cyclization of ureidoacetamide: A novel route towards the synthesis of 2,4,5-trisubsituted oxazoles

A variety of N, 2-diaryl-2-ureidoacetamide prepared from the condensation of N-aryl-α-aminoamide with potassium cyanate (KOCN) undergo efficient Hendrickson’s reagent-mediated nucleophilic cyclization to afford 2,5-diamine-4-aryloxazoles. The two-step synthesis provides seven target products in yields of 61–78% under mild conditions. This reaction involves an unusual pathway in which the electrophilic amide carbonyl carbon is activated by Hendrickson’s reagent and attacked by a nucleophilic ureido oxygen in a 5-exo-trig O-cycloisomerization.     

New synthesis of the dihydroindolizinoquinoline system by intramolecular cyclization of sulfur ylide

An efficient method is proposed for obtaining the dihydroindolizinoquinoline system by intramolecular cyclization of keto-stabilized sulfonium ylide obtained from -alanine and quinoline-2,3-dicarboxylic acid anhydride.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1813–1816, December, 2004.     

Sulfur ylides 13. Synthesis and intramolecular cyclization of keto-stabilized sulfur ylides

Keto-stabilized sulfur mono-and bisylides were obtained from N-phthalylglutamic acid and their intramolecular cyclization was studied. The intramolecular cyclization of the ylide obtained at the α-carboxy group gave a product of the pyrrolizidinedione structure; bisylide yielded a cycloheptene derivative as the result of intramolecular recombination of intermediate dicarbene. The ylide obtained at the γ-carboxy group underwent no cyclization, giving methylthio ketone and oxo benzoate. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2771–2776, December, 2005.     

Mass spectrometry of nitrogen heterocycles. 3. Thermal intramolecular cyclization of 2-azolylaminopyridines

Mass spectrometric fragmentation or decay of 2-azolylaminopyridines containing a carbonyl group in the ortho-position results in elimination of a neutral molecule (ammonia, ethanol, hydrogen sulfide). This decay process is accompanied by intramolecular cyclization to form an ion with a triazolo[1,5-a]pyrido[2,3-d]pyrimidine structure.For Communication 2, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 101–104, January, 1991.     

A Dieckmann cyclization route to piperazine-2,5-diones

Piperazine-2,5-diones are formed by Dieckmann cyclization (NaH, THF) of substructures of the type CH(2)-N(R)C(O)CH(2)N(R')CO(2)Ph in which the terminal methylene (CH(2)) that is adjacent to nitrogen closes onto the carbonyl group of the phenyl carbamate unit at the other end of the chain. R and R' are alkyl groups, and the terminal methylene is activated by a ketone carbonyl, a nitrile, an ester, or a phosphoryl group. The starting materials are assembled by standard acylation and oxidation processes, starting from a β-(alkylamino)alcohol, an (alkylamino)acetonitrile, an (alkylamino) ester, or an (alkylamino)methyl phosphonate.