CO2 capture capacity of five- and six-membered cyclic amidines bearing silatranyl group under dry conditions

CO₂ capture and release behaviors of three amidines bearing silatranyl group in DMSO solution were evaluated under dry conditions containing a very small amount of water. A six-membered cyclic amidine with silatranyl group captured CO₂ at 25 °C under atmospheric pressure quantitatively, and the trapped CO₂ was released at 60 °C under Ar atmosphere. A five-membered cyclic amidine with silatranyl group also captured CO₂, but less efficiently, under the same conditions as above. In contrast, an acyclic amidine with silatranyl group did not capture CO₂ at all, as expected from the poor CO₂-capturing ability of the acyclic amidine moiety.     

Synthesis of five- and six-membered lactams via solvent-free microwave Ugi reaction

Five- and six-membered lactams were synthesized via a 4-center 3-component Ugi reaction by combining amines, isocyanides, and ketoacids under solvent-free microwave conditions. The reaction was carried out in much shorter times and the yields were improved in comparison to classical conditions.     

A synthesis of aromatic five- and six-membered B-N heterocycles via ring closing metathesis

The ring closing metathesis on appropriate vinyl or allyl aminoboranes (1 or 2) gives azaboracycloalkenes (3 or 4) which can be converted to azaborolides (5) or azaborines (6).     

A direct synthesis of α-keto five- and six-membered cyclic ethers

A simple synthesis of tetrahydro-2H-pyran-2-yl and tetrahydrofuran-2-yl ketones from their corresponding carboxylic acids was studied. A comparison was made of organolithium and Grignard alkylating reagents as a means of reducing the formation of byproducts and improving the yields.     

Synthesis of five- and six-membered cyclic guanidines by guanylation with isothiouronium iodides and amines under mild conditions

Cyclic guanidine hydroiodides were obtained in one step by the reactions of isothiouronium iodides with an equimolar amount of various amines in tetrahydrofuran. The obtained hydroiodides were neutralized with sodium hydroxide or anionic exchange resin to afford the corresponding substituted cyclic guanidines in quantitative yields.     

Selective formation of six-membered cyclic sulfones and sulfonates by C-H insertion

[reaction: see text] Carbethoxy diazosulfones and sulfonates, easily available from corresponding sulfones and sulfonates, undergo C-H insertion with preferential formation of six membered cyclic sulfones and sulfonates.     

Synthesis of benzo-fused five- and six-membered heterocycles by palladium-catalyzed cyclocarbonylation

A novel and simple synthetic methodology, based on palladium-catalyzed cyclocarbonylation reaction, is presented for preparing five- and six-membered benzo-fused heterocycles. A mechanism for the process is also proposed and discussed.     

The mass spectra of spiro-alkanones with five- and six-membered rings

The mass spectral fragmentations of three spiro-undecanones and four dispiro-hexadecanones with six-membered rings, and of two spiro-nonanones with five-membered rings are recorded and discussed. The fragmentation patterns for the spiro[4,4]nonanones and the spiro[5,5]undecanones have been determined by using specific deuterium labelling and in some cases the measurement of metastable transitions by the defocusing technique. The most important fragment ions in the spectra of four dispiro-hexadecanones could be explained by assuming the same types of fragmentation as found for the monospiro-ketones. The composition of the fragment ions has been checked by high resolution mass measurements.     

Formation of five- and six-membered heterocyclic rings under radical cyclisation conditions

This review describes the formation of five- and six-membered heterocyclic rings in various organic molecules by radical cyclisation and covers mostly the literature published in 2005.     

A stereoselective and atom-efficient approach to multifunctionalized five- and six-membered rings via a novel michael-initiated intramolecular Diels-Alder furan reaction

[reaction: see text] A variety of key precursors to the intramolecular Diels-Alder reaction of furan diene (IMDAF) have been prepared via a very facile 1,4-addition of O-, S-, N-, and C-centered nucleophiles possessing unsaturated tether to beta-furyl nitroethylene. Subsequent IMDAF reaction of the 1,4-adducts, carried out under thermal conditions, provided five- and six-membered carbocycles and heterocycles fused to an easily cleavable oxabicycloheptene moiety. The structure and stereochemistry of the cycloadducts were determined by 2D-NMR experiments and further confirmed by X-ray crystallography. The salient features of the strategy include high degree of stereoselectivity (>80:20) in the cycloaddition, atom and step economy, and generation of multiple chiral centers and functionalities. The feasibility of the cleavage of the oxa bridge in the cycloadducts to afford novel multifunctional molecules has also been demonstrated.     

PMR spectra of some five- and six-membered heterocyclic compounds of silicon and germanium

The PMR spectra of various 1-sila- and 1-germacyclopentanes and also those of some substituted disilacyclohexanes are discussed. The influence of the magnetic field of the aryl and vinyl substituents in 1,1-dialkyl-2,5-diaryl(vinyl)-1-sila(germa)cyclopentanes on the chemical shifts of the protons of the individual groups is studied, the differences found in the position of the PMR lines of the methyl and methylene groups showing the existence of cis-trans isomers in these heterocycles. With 1,1-dimethyl-2,5-divinylsilacyclopentane as an example, an increase in screening due to the magnetism of the multiple bonds for the protons of groups not directly connected with the unsaturated groupings and located in a direction perpendicular to the axis of the double bond has been found experimentally.Lecture at the XI-th Scientific Conference of the Institute of High-Molecular-Weight Compounds of the Academy of Sciences of the USSR (Leningrad, March, 1964) and at the All-Union Conference on the Use of Radiospectroscopy in Chemistry (Moscow, January, 1965).The authors express their gratitude to A. V. Kessenikh for taking several of the PMR spectra and for critical observations on the investigation.     

Generation and properties of episulfonium intermediates. 7. Generation of episulfonium ions from 1,3-butadiene and isoprene

Conclusions It has been shown to be possible to generate episulfonium intermediates by reacting divinyl or isoprene with a variety of arylsulfenyl cations. The formation of these intermediates and their reaction with the acetate anion occurs with strict regioselectivity, attacking only one of the double bonds of the diene system.For part 6, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2300–2306, October, 1979.     

Recent developments in the synthesis of five- and six-membered heterocycles using molecular iodine

Heterocyclic scaffolds represent the key structural subunits of many biologically active compounds. Over the last few years iodine-mediated reactions have been extensively studied due to their low cost and eco-friendliness. This Review covers advances in the field of iodine-mediated synthesis of heterocyclic compounds since 2006, especially with an emphasis on mechanisms of ring formation. In this article, syntheses of different heterocycles are classified based on the manipulation of functional groups.     

Asymmetric one-pot synthesis of five- and six-membered lactones via dynamic covalent kinetic resolution: Exploring the regio- and stereoselectivities of lipase

Cascade lipase-catalyzed lactonization has been applied to dynamic hemithioacetal formation, leading to efficient five- and six-membered lactone synthesis as well as chiral discrimination. Solvent-dependent regioselectivity was observed for the selective formation of 1,3-oxathiolan-5-one and γ-butyrolactone derivatives.     

Detailed study of the ring-opening metathesis polymerization of norbornene bearing a five- or six-membered ring cyclic carbonate along with volume expansion

The ring-opening metathesis polymerization (ROMP) of norbornene derivatives bearing five- or six-membered cyclic carbonate ( 2 or 3 ) was carried out with a typical ruthenium catalyst [bis(tricyclohexylphosphine)benzylidene ruthenium(IV) dichloride], the so-called first-generation Grubbs catalyst, under various reaction conditions, to smoothly obtain the corresponding polyalkenamers ( 5 and 6 ) along with volume expansion. The number-average molecular weights (M_n's), 10% weight loss decomposition temperatures, glass-transition temperatures (T_g's), and volume expansion ratios of the resulting products depended on the polymerization conditions. The degree of volume expansion was mainly affected by M_n, T_g, and the cis/trans configuration of the exocyclic double bonds of the resulting polymers. The volume expansion was confirmed to specifically occur during the polymerization of the monomer bearing cyclic carbonate moieties, and similar ROMPs of monomers without cyclic carbonate, such as norbornene itself, the monomer 5,5-bis(methoxymethyl)bicyclo[2.2.1]hept-2-ene, and the monomer endo-N-methylbicyclo[2.2.1]hept-5-ene-2,3-dicarboxylimide, proceeded along with volume shrinkage. Furthermore, an investigation of another type of polymerization, a vinyl-type one, of monomer 2 suggested that the volume expansion specifically took place in the ring-opening type of polymerization. In addition, the Sc(OTf)₃-mediated cationic ring-opening reaction of the cyclic carbonate moiety of polyalkenamer 5 smoothly proceeded along with volume expansion or nearly zero volume shrinkage to yield the corresponding networked polymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 395–405, 2006     

Chiral anion-mediated asymmetric ring opening of meso-aziridinium and episulfonium ions

Reactions proceeding through cationic intermediates that lack a Lewis or Br?nsted basic site present a challenge for traditional asymmetric catalysis based on chiral metals or organocatalysts. We present an enantioselective ring opening of tetrasubstituted meso-aziridinium ions with alcohol nucleophiles proceeding through a chiral ion pair with a binaphthol-phosphate anion. The reaction is initiated by silver-induced ring closure of beta-chloroamines using the Ag salt of the chiral anion as in situ generated catalyst. Use of insoluble Ag2CO3 as silver source is essential to obtain high enantioselectivity; we believe the chiral phosphate acts as a "chiral anion phase transfer catalyst" to bring silver ion into the organic phase. The chiral anion concept can also be extended to the related asymmetric opening of meso-episulfonium ions generated by protonation of trichloroacetimidates vicinal to sulfides.     

Conformational analysis of six-membered cyclic carbonates

The conformational isomerization of 2-oxo-1,3-dioxane and its methyl analogs was investigated by means of ab initio RHF//6-31G(d,p) and MP2//6-31G(d,p) quantum-chemical methods. It is shown that in comparison with 1,3-dioxanes the potential energy surface of the mentioned compounds has a fewer number of stationary points and includes two minima corresponding to conformers of sofa or distorted sofa configuration and one maximum corresponding to 2,5-twist form. The value of potential barrier of interconversion of cyclic carbonates is significantly lower than that of the analogously substituted 1,3-dioxanes.