Convenient synthesis of 1,2,3,4-tetrahydroquinolines via direct intramolecular reductive ring closure

A simple and convenient procedure for the synthesis of 3-aryl-1,2,3,4-tetrahydroquinolines is reported. 3-Aryl-1,2,3,4-tetrahydroquinolines are directly obtained by reductive ring closure of 2-phenyl-3-(2-nitrophenyl)-propionitrile derivatives in moderate to high yields.     

Preferential intramolecular ring closure of aminoalcohols with diethyl carbonate to oxazolidinones

The closure by cyclization with diethyl carbonate (EtO)(2)CO from aminoalcohols 1 as starting material can lead to the oxazolidinones 2a, b and 2c, respectively. In the reaction of trans-isomer (6) and (EtO)(2)CO, isolated products were also only 5-membered oxazolidinone derivative (7), containing its dehydrated derivative 8. The preferential formation of the 5-membered oxazolidinone ring system apparently indicated that this process (5-Exo-Trig ring closure) is more favorable than that of 6- or 7-membered ring derivative (3 or 9) by 6- or 7-Exo-Trig ring closure.     

Asymmetric synthesis of orthogonally protected trans-cyclopropane gamma-amino acids via intramolecular ring closure

The synthesis of enantiomerically-enriched trans-cyclopropane amino- and hydroxy-acids can be achieved by intramolecular ring closure in moderate to good yields. The optically active cyclopropane precursors are easily prepared in a short sequence from inexpensive, commercially available olefins and tert-butyl acetate. Several leaving groups and bases were compared for the cyclopropanation step, showing that the diphenylphosphinate and tosyl leaving groups give the best results when used in combination with either LDA or NaHMDS.     

Rules for ring closure: application to intramolecular aldol condensations in polyketonic substrates

An extension of the nomenclature for classifying ring closures to include intramolecular reactions of enolate anions is described, and the rules governing such cyclizations are enumerated. The syntheses of the polyketonic substrates 4-acetyl-2,6-heptanedione (11), 4-acetyl-4-methyl-2,7-octanedione (24), and 3-acetyl-3-methyl-1,6-diphenyl-1,6-heptanedione (33) were carried out, and their base-induced intramolecular aldol condensations studied. With each substrate a favored 6-(enolendo)-exo-trig cyclization to produce cyclohexenone products was the only ring forming reaction observed, this process predominating in all instances over competing disfavored 5-(enolendo)-exo-trig closures, and also over other competing favored cyclizations. The identity of the cyclization product 12 derived from 11 was confirmed by aromatizing 12 to 17, and alternately synthesizing 17 from 3-bromo-5-methylphenol.     

Electrochemically driven formation of a molecular capsule around the ferrocenium ion

Electrochemical experiments were used to show that the oxidation of ferrocene triggers the self-assembly of six molecules of the resocin[4]arene 2 to form a molecular capsule around the oxidized, ferrocenium (+1) form. The nature of the supporting electrolyte anion is crucial for this process of electrochemically driven self-assembly. 1H NMR spectroscopic data obtained with cobaltocenium, a diamagnetic analogue of the paramagnetic ferrocenium ion, verify its encapsulation by six molecules of 2. The encapsulation of cobaltocenium was also observed in voltammetric experiments. Encapsulation of ferrocenium (or cobaltocenium) inside the large 26 capsule led to a dramatic slowing of its usually fast, one-electron electrochemical reduction to ferrocene (or cobaltocene).     

Electrochemically driven reagent release from an electronic suture

Sutures loaded with growth factors or antimicrobials are commonplace but the release of the therapeutic agent is almost invariably achieved through passive release mechanisms. A gold microwire loaded with cellulose acetate phthalate encapsulated drug droplets is proposed as an alternative design approach. The release mechanism relies upon the imposition of a suitable reducing potential at the gold suture resulting in an increase in local pH and thereby induces the dissolution of the polymeric binder and releases the drug. The ability to actively control the dissolution-release processes could lay the foundations for smart suture design where more responsive/metered dosing could be achieved.     

Electrochemically initiated intramolecular cyclization of 2-nitro-2′-isothiocyanatobiphenyl

2-Nitro-2′-isothiocyanatobiphenyl was prepared as a new substance, suitable for the investigation of an electrochemically initiated intramolecular cyclization. If it is reduced at a mercury cathode in acidic media an acid catalysed intramolecular follow-up reaction occurs which leads to the formation of 6-mercaptodibenzo (d, f)-(1,3)-diazepin-5-oxide. The rate of the follow-up reaction decreases in neutral or alkaline media and the reduction of the isothiocyanato group also takes place. The main product is here 5,6-dihydrobenzo(c)cinnoline.     

Furan ring opening-isochromene ring closure: a new approach to isochromene ring synthesis

A new approach toward the synthesis of 1H-isochromenes based on the recyclization of the furan ring in the corresponding ortho-hydroxymethylbenzylfurans is described.     

Synthesis of some ω- (2,5-dichloro-3-thienyl)alkanoic acids and their intramolecular ring closure

The synthesis of 1-chloro-4,5,6,7-tetrahydrobenzo[c]-4-thiophenone and 1-chloro-5,6,7,8-tetrahydro-4H-cyclohepta[c]-4-thiophenone was accomplished by the cyclization of the acid chlorides of -(2,5-dichloro-3-thienyl)butyric acid and -(2,5-dichloro-3-thienyl)valeric acid, respectively, to 1,3-dichloro-4,5,6,7-tetrahydrobenzo[c]-4-thiophenone and 1,3-dichloro-5,6,7,8-tetrahydro-4H-cyclohepta[c]-4-thiophenone and by partial dehalogenation of the latter by heating with copper metal in propionic acid.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1358–1360, October, 1971.     

Electrochemically driven intrusion of silver particles into silicon under polarization

The pore formation with the diameter of around 100 nm into a lightly doped p-type Si was achieved with the intrusion of silver particles by electrolysis in HF aqueous solution. The route resembles the metal-catalyzed electroless pore formation, but the present method uses anodic polarization instead of chemical etching in the presence of oxidizing agent. A microporous layer was observed around the pores formed as the tracks of silver particles. Thickness of the microporous layer around the track increased with the increase in current density. The thickness was varied in accordance with the time-programmed variation of current density. Conversely, the intrusion of silver particles seldom occurred in heavily doped p-type silicon, while micropores were formed independently of the location of the particles. The concentration of dopant affects the silver-particle-assisted porosification.     

The use of sodium hydride in a ring closure

The use of sodium hydride for the synthesis of 1,5-methano-3-benzazocine derivatives, which involves the intramolecular acylation of the α-methylene group of tetralone by methylene isocyanate substituents, is discussed in detail.     

An unprecedented radical ring closure on a pyridine nitrogen

An unprecedented radical ring-closure onto the pyridine nitrogen was observed when certain types of substituents were present around the pyridine nucleus.     

Cyclobutanones through SNi' ring closure, a mechanistic study

Mechanistic studies on the intramolecular nucleophilic substitution with allylic rearrangement (SNi' reaction) and a new stereoselective access to substituted cyclobutanones are reported. 4,4-Dialkyl-5-oxohex-2E-en-1-yl methanesulfonates 4 were converted to 2,2-dialkyl-3-vinylcyclobutanones 6 by SNi' ring closure. The stereochemical analysis of the reaction was achieved through ring closure of (6S)-6-chloro-3,3-diethylhept-4E-en-2-one (S)-17, defined by the absolute configuration of C(6), leading to (3S)-2,2-diethyl-3-(prop-1E-en-1-yl)cyclobutanone (S)-(E)-18 and (3R)-2,2-diethyl-3-(prop-1Z-en-1-yl)cyclobutanone (R)-(Z)-18, in a ratio of 85:15, with almost complete transfer of chirality (>97%). The absolute configuration of (S)-17 was determined by X-ray diffraction analysis of the camphanoate derivative 16. The absolute configuration of the cyclobutanone products (S)-(E)-18 and (R)-(Z)-18 was determined by Raman optical activity spectroscopy. Comparison of the absolute configuration of (S)-17 and the resulting (E)- and (Z)-cyclobutanones 18 allowed the conclusion that the SNi' reaction proceeds with syn geometry relative to the leaving group.     

Electrochemically driven clathration/declathration of ferrocene and its derivatives by a nanometer-sized coordination cage

The electrochemical, NMR, and crystallographic studies clearly indicate that the clathration and declathration of ferrocene and its derivatives in a self-assmbled Pd(II)-linked nanometer-sized cage can be controlled by the oxidation state of the guest. Namely, the guests are clathrated when they are reduced but declathrated when they are oxidized. The process is rapid on the NMR time scale but slow on the CV time scale.     

The ring closure of 5-methylcyclopenta-1,3-dien-5-ylcarbene to 1-methylbenzvalene. An intramolecular 1,4 cheletropic carbene addition

The title carbene ($\text{7}$) is shown to produce the benzvalene skeleton by stereospecific intramolecular 1,4 addition and not by classic cyclopropanation.