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Ring-closure Reaction (ring-closure + reaction)
Selected AbstractsRing-Closure Reactions through Intramolecular Displacement of the Phenylselenonyl Group by Nitrogen Nucleophiles: A New Stereospecific Synthesis of N -Tosyl and N -Benzoyl-1,3-oxazolidin-2-ones from ,-Hydroxyalkyl Phenyl SelenidesCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2004Marcello Tiecco Prof. Abstract A new and convenient method for the stereospecific synthesis of variously substituted 1,3-oxazolidin-2-ones from the easily available ,-hydroxyalkyl phenyl selenides is presented. After transformation into the N -tosyl or N -benzoyl carbamates, the selenides were oxidized to the corresponding selenones. The key step of the process is the ring-closure reaction, which occurs by stereospecific intramolecular nucleophilic substitution of the selenone group by the nitrogen atom of the carbamate. Enantiomerically pure 1,3-oxazolidin-2-one derivatives can be easily prepared by using enantiomerically pure ,-hydroxyalkyl phenyl selenides as starting materials. [source] Novel Synthesis of 4H -Quinolizine Derivatives Using Sulfonyl Ketene DithioacetalsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 33 2009Masayori Hagimori Abstract In the synthesis of 4H -quinolizine derivatives involving the use of a sulfonyl ketene dithioacetal, we found a novel reaction in which the remaining methylsulfanyl group was replaced with a proton after the ring-closure reaction in the quinolizine skeleton under mild conditions, without the use of any metallic reagent. The reaction of 3,3-bis(methylsulfanyl)-2-phenylsulfonylacrylonitriles (1a,b) with 2-pyridylacetonitrile (2a) in the presence of potassium carbonate as a base in DMSO afforded 4-imino-2-methylsulfanyl-3-phenylsulfonyl-4H -quinolizine-1-carbonitriles (3a,b). The methylsulfanyl group at the 2-position of 3a,b was readily removed under methanol reflux conditions to afford 4-imino-3-phenylsulfonyl-4H -quinolizine-1-carbonitriles (4a,b) in good yields. Alkyl 3-phenylsulfonyl-4H -quinolizine-1-carboxylates (4c,f) were directly synthesized from sulfonyl ketene dithioacetal (1a,b) with alkyl 2-pyridylacetates (2b,c) and involved desulfanylation by simple hydrolysis. In addition, the fluorescent properties of these compounds were investigated. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Asymmetric Synthesis of (S)-Mirtazapine: Unexpected Racemization through an Aromatic ipso -Attack MechanismEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2008Marco van der Linden Abstract An asymmetric synthesis of (S)-mirtazapine has been achieved from the synthesis of the racemate by using (S)-1-methyl-3-phenylpiperazine as the starting material. Unfortunately, significant racemization was encountered in the final step, which involved an electrophilic aromatic ring closure of a alcohol by concentrated sulfuric acid. A significantly higher ee was observed when polyphosphoric acid (PPA) was used instead. A remarkable correlation between the amount of PPA used and the ee of the product was revealed, namely, an increase in the ee upon decreasing the amount of PPA. This trend was paralleled by the formation of an increasing amount of a side-product upon lowering the amount of PPA. The racemization and formation of a side-product can be explained by an ipso -attack mechanism during the electrophilic aromatic ring-closure reaction. This mechanism was supported by a mechanistic study using a deuterium-labeled substrate.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Synthesis of 1,3-Difunctionalized Cyclopentenes and 1,3,5-Trifunctionalized Cyclohexanes by Silicon-Induced Domino ReactionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2003Frank Tries Abstract A novel domino process based on a 1,4-C,O shift of a silyl group (4 , 3) and a Michael-induced ring-closure reaction (3 , 2) is investigated. Specifically, attack of carbanions 5 on vinyloxiranes 6 usually occurs on the oxirane unit to give the desired silyl shift. When starting from vinyloxiranes 6a and 6b, however, the reaction stops at this stage to give silyl ethers 7. Sulfur (6c) or silicon activation (6d,f) of the C=C unit is required to yield cyclopentenes 1a,d. Analogously, carbanion 5a and allyloxiranes 15 give cyclization products 19,22, particularly if the ring-closure step is supported by silicon substitution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Triplet MLCT Photosensitization of the Ring-Closing Reaction of Diarylethenes by Design and Synthesis of a Photochromic Rhenium(I) Complex of a Diarylethene-Containing 1,10-Phenanthroline LigandCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2006Chi-Chiu Ko Dr. Abstract Synthesis of the diarylethene-containing ligand L1 based on Suzuki cross-coupling reaction between thienyl boronic acid and the dibromophenanthroline ligand is reported. On coordination to the rhenium(I) tricarbonyl complex system, the photochromism of L1 could be photosensitized and consequently extended from intraligand excitation at ,,340 nm in the free ligand to metal-to-ligand charge-transfer (MLCT) excitation at ,,480 nm in the complex. The photochromic reactions were studied by 1H NMR, UV/Vis, and steady-state emission spectroscopy. Photosensitization was further probed by ultrafast transient absorption and time-resolved emission spectroscopy. The results provided direct evidence that the formation of the closed form by the MLCT-sensitized photochromic process was derived from the 3MLCT excited state. This supports the photosensitization mechanism, which involves an intramolecular energy-transfer process from the 3MLCT to the 3IL(L1) state that initiated the ring-closure reaction. The photophysical and electrochemical properties of the complex were also investigated. [source] Ring-Closure Reactions through Intramolecular Displacement of the Phenylselenonyl Group by Nitrogen Nucleophiles: A New Stereospecific Synthesis of N -Tosyl and N -Benzoyl-1,3-oxazolidin-2-ones from ,-Hydroxyalkyl Phenyl SelenidesCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2004Marcello Tiecco Prof. Abstract A new and convenient method for the stereospecific synthesis of variously substituted 1,3-oxazolidin-2-ones from the easily available ,-hydroxyalkyl phenyl selenides is presented. After transformation into the N -tosyl or N -benzoyl carbamates, the selenides were oxidized to the corresponding selenones. The key step of the process is the ring-closure reaction, which occurs by stereospecific intramolecular nucleophilic substitution of the selenone group by the nitrogen atom of the carbamate. Enantiomerically pure 1,3-oxazolidin-2-one derivatives can be easily prepared by using enantiomerically pure ,-hydroxyalkyl phenyl selenides as starting materials. [source] Synthesis of 2,4-Diaryl-3,4-dihydro-2H - naphth[2,1- e][1,3]oxazines and Study of the Effects of the Substituents on Their Ring - Chain TautomerismEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2004István Szatmári Abstract A number of 2-(,-amino-Y-substituted-benzyl)-1-naphthol hydrochlorides were prepared by a convenient Mannich-type aminoalkylation. 2,4-Diaryl-3,4-dihydro-2H -naphth[2,1- e][1,3]oxazines were prepared through the ring-closure reactions of the starting aminonaphthols with aromatic aldehydes, which proved to furnish three-component (ring1,open,ring2) tautomeric mixtures in CDCl3 at 300 K. The electronic effects of the 2-aryl groups on the ratios of the ring - chain tautomeric forms at equilibrium could be described by Equation (1). Study of the effects of substituents X and Y on the tautomeric equilibria [by the aid of the multiple linear regression analysis of Equations (2) and (3)] revealed that the trans -chain equilibrium constants are significantly influenced by the inductive effect (,F) of substituent Y on the 4-phenyl ring. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Synthesis of Highly Functionalized , -Lactones via 1,5-Electrocyclic Ring ClosureHELVETICA CHIMICA ACTA, Issue 6 2006Olcay Anaç Abstract We have investigated 1,5-electrocyclic ring-closure reactions of conjugated esters with dimethyl diazomalonate in the presence of [Cu(acac)2] as catalyst. Our new protocol offers an easy entry to various polyfunctionalized , -lactones in high yields. Their subsequent derivatives may be used as valuable intermediates, especially in the synthesis of natural products and their analogues. [source] | ||||||||||