Search results for " cyclization"

Oxidative cyclization reaction of 2-aryl-substituted cinnamates to form phenanthrene carboxylates by using MoCl5.

2014

The oxidative cyclization reaction of 2-aryl cinnamates and derivatives thereof can be easily performed with MoCl5 as the oxidant. This powerful reagent allows oxidative coupling reactions for which other reagents fail. The best results are obtained when the 2-phenyl substituent of the cinnamate is equipped with two methoxy groups. Even iodo moieties in the bay region of phenanthrene are tolerated under the reaction conditions. If naphthalene moieties are involved, a rearrangement of the skeleton occurs, providing an elegant route to highly functionalized angular arenes. The cyclization is demonstrated for 15 example substrates with isolated yields of up to 99 % for the phenanthrene derivat…

Oxidative Coupling Reactions of 1,3-Diarylpropene Derivatives to Dibenzo[a,c]cycloheptenes by PIFA

2011

The oxidative cyclization reactions of a variety of α-benzyl-cinnamates can be selectively performed with hypervalent iodine as an oxidant. The dibenzo[a,c]cycloheptenes were isolated in up to 55 % yield. When an oxo substrate is applied, the yield was significantly increased. With this synthetic approach, a central intermediate for the synthesis of metasequirin-B was obtained in three steps from very simple starting materials. For this transformation, both aryl moieties have to be activated.

Cover Picture: Oxidative Cyclization Reaction of 2-Aryl-Substituted Cinnamates To Form Phenanthrene Carboxylates by Using MoCl5 (Chem. Eur. J. 39/201…

2014

A quantitative study of substituent effects on oxidative cyclization of some 2-methylsubstituted aldehydes. Thiosemicarbazones induced by ferric chlo…

1996

In order to gain further mechanistical information about the cyclization of thiosemicarbazones and thiosemicarbazone-type substrates induced by metallic salts as oxidizing agents, we performed the synthesis of substrates 1a-s and a kinetic study of the oxidative cyclization of 1 to 5-imino-Δ2-1,3,4-thiadiazole 2 and 1,2,4-triazoline-5-thione 3 derivatives induced by methanolic ferric chloride solutions. The results of cyclization were compared to those of corresponding semicarbazones. The kinetic data were analyzed by means of the Hammett's equation and ρ values discussed.

ChemInform Abstract: A Quantitative Study of Substituent Effects on Oxidative Cyclization of Some 2-Methylsubstituted Aldehydes. Thiosemicarbazones I…

2010

In order to gain further mechanistical information about the cyclization of thiosemicarbazones and thiosemicarbazone-type substrates induced by metallic salts as oxidizing agents, we performed the synthesis of substrates 1a-s and a kinetic study of the oxidative cyclization of 1 to 5-imino-Δ2-1,3,4-thiadiazole 2 and 1,2,4-triazoline-5-thione 3 derivatives induced by methanolic ferric chloride solutions. The results of cyclization were compared to those of corresponding semicarbazones. The kinetic data were analyzed by means of the Hammett's equation and ρ values discussed.

ChemInform Abstract: Oxidative Cyclization Reaction of 2-Aryl-Substituted Cinnamates to Form Phenanthrene Carboxylates by Using MoCl5.

2015

The reagent mixture MoCl5/TiCl4 is successfully applied for the oxidative cyclization of α-aryl substituted cinnamates to the corresponding phenanthrenes.

Radical Cyclization and 1,5-Hydrogen Transfer in Selected Aromatic Diazonium Salts

2014

2-(Methyl(3-methyl-1-phenyl-1H-pyrazol-5-yl)carbamoyl)thiophene-3-diazonium hydrogen sulfate 20, 2-(methyl(3-methyl-isoxazol-5yl)carbamoyl)-benzenediazonium hydrogen sulfate 21 and 2-(methyl(phenyl)carbamoyl)-benzenediazonium hydrogen sulphate 22 were synthesized and reacted with a CuSO4/NaCl/ascorbic acid combination to give complex mixtures. The structures of the reaction products were elucidated, depending upon the pathways followed. Compound 20 almost exclusively afforded an Ar-5 cyclization product and trace amounts of the product derived from a competing Ar-6 Pschorr closure. In the case of compound 21, the Ar-6 cyclization was not observed, while the Ar-5 cyclization and 1,5-hydrogen…

Synthesis of a bridgehead nitrogen system. Imidazo[1,5-b]pyridazine derivatives

1979

3,4-Dibenzoyl-2-oxobutyrate 4-semicarbazone (6a), ethyl 2,4-dioxo-3-phenacylvalerate 3-semicarbazone (6b) and diethyl phenacyloxalectate 3-semicarbazone (6c) via acid catalysed intramolecular cyclization afforded 2-phenyl-4-R-3H-imidazo[1,5-d]pyridazine-5,7-(6H)diones (8d,e,f). Elemental analyses and spectroscopic data (ir, nmr, ms) were in good agreement with the assigned structures.

Ir-Catalyzed Cycloaddition of Tribenzocyclyne with Biphenylenes

2021

We demonstrate that Ir-catalyzed C-C bond activation in biphenylenes followed by a reaction with tribenzocyclyne is a suitable method for synthesizing strained and unknown monoadducts with the tetradehydrotetrabenzo[a,c,e,i]cyclododecene scaffold ([12]annulenes). Modification of reaction conditions also furnished [12]annulene products with cis and/or trans double bonds formed by hydrogen transfer. The [9]annulene side product was formed upon the reaction of the benzyl radical with tribenzocyclyne during the Bergman cyclization. All isolated compounds were fully characterized by HRMS, NMR, and X-ray diffraction analysis.

The Reaction Mechanism of Spirocylization and Stereoselectivity Studies for the Calyculin C16 -C25 Fragment

2005

The mechanism of the double intramolecular hetero-Michael addition, a key reaction in the planned synthesis of the natural product calyculin C, has been studied by NMR. The cyclization follows Baldwin’s rules and proceeds first through a six-membered ring closure (6-endo-dig), followed by a five-membered ring cyclization (5-exo-trig). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)