Cross-metathesis reaction of vinyl sulfones and sulfoxides

Cross-metathesis reactions of α,β-unsaturated sulfones and sulfoxides in the presence of molybdenum and ruthenium pre-catalysts were tested. A selective metahesis reaction was achieved between functionalized terminal olefins and vinyl sulfones by using the ‘second generation’ ruthenium catalysts 1c-h while the highly active Schrock catalyst 1b was found to be functional group incompatible with vinyl sulfones. The cross-metathesis products were isolated in good yields with an excellent (E)-selectivity. Both the molybdenum and ruthenium-based complexes were, however, incompatible with α,β- and β,γ-unsaturated sulfoxides.     

Studies on hydrozirconation of 1-alkynyl sulfoxides or sulfones and the application for the synthesis of stereodefined vinyl sulfoxides or sulfones

The hydrozirconation reaction of 1-alkynyl sulfoxides or sulfones with Cp2Zr(H)Cl in THF at room temperature predominantly gave Z-beta-zirconated vinyl sulfoxides or sulfones with excellent regioselectivity. Compared with 1-alkynyl sulfoxides, the hydrozirconation reaction of 1-alkynyl sulfones exhibits great synthetic potential, leading to the efficient preparation of Z-beta-halovinyl sulfones, Z-beta-sulfonyl alpha,beta-unsaturated ketones, and Z-beta-alkynyl vinyl sulfones. Although the reaction mechanisms are still not clear, the neighboring group participation of the sulfinyl or sulfonyl group may be playing an important role in this unique hydrozirconation reaction.     

A comparison of hydrogen bonding solvent effects on the singlet oxygen reactions of allyl and vinyl sulfides, sulfoxides, and sulfones

The singlet oxygen (¹Δ_g) photooxidations of 2-methyl-3-phenylthio-2-butene (1a), 1-[(4-nitrophenyl)thio]-2,3-dimethyl-2-butene (2c), 2-methyl-3-phenylsulfinyl-2-butene (3), 2-methyl-3-phenylsulfonyl-2-butene (6), and 1-[(4-nitrophenyl)sulfonyl]-2,3-dimethyl-2-butene (7c) were conducted in the following deuterated solvents: acetonitrile, benzene, chloroform, methanol, or methanol/water mixture. In each case the ene allylic hydroperoxide products and/or the [2+2] cycloaddition products were quantified and inspected for possible hydrogen bonding induced differences in product selectivity and regiochemistry. After comparison to literature values for related substrates, the results indicate that only photooxidations of vinyl sulfides are susceptible to hydrogen bonding solvent effects.     

Thermal (1,3)-allylic rearrangements in sulfoxides and sulfones

Rates and activation parameters for thermal (1,3)-allylic rearrangement have been determined for the systems β-methylallyl phenyl sulfoxide ($\text{2}$) and the corresponding sulfone ($\text{3}$), with evidence presented for a dissociative reaction mechanism.     

Selective synthesis of sulfoxides and sulfones by tantalum(V) catalyzed oxidation of sulfides with 30% hydrogen peroxide

The reaction of sulfides with 30% hydrogen peroxide catalyzed by tantalum(V) chloride in acetonitrile, i-propanol, or t-butanol selectively provided the corresponding sulfoxides in high yields. On the other hand, the reaction of sulfides with 30% hydrogen peroxide-catalyzed by tantalum(V) chloride or tantalum(V) ethoxide in methanol effectively gave the sulfones.     

Topological study of intramolecular hydrogen bonding in beta-hydroxyethylperoxy radical and beta-hydroxyethoxy radical along its dissociation pathway

The presence of intramolecular hydrogen bond (IHB) in beta-hydroxyethylperoxy and beta-hydroxyethoxy radicals was investigated using the QTAIM topological study on UB3LYP/6-311++G(2d,2p) charge densities. Only one of the two conformers of beta-hydroxyethylperoxy radical which were previously considered to present IHB displays a bond critical point (BCP) associated to an IHB. Furthermore, the atomic energies and electron populations indicate no evidence of IHB in the second conformer. Nevertheless, very small differences in molecular energies were obtained using several one-step and multi-step methods (G3, G3B3) between both conformers. No BCP is found between the hydroxyl hydrogen and the oxygen in the most stable conformer or in the transition state for the dissociation path of beta-hydroxyethoxy radical. However, a BCP is formed in the last steps of this path, thereby yielding H-bonded products.     

Synthesis of dinitrosyl iron complexes (DNICs) with intramolecular hydrogen bonding

HSCH₂CONHCH₃ and HSCH₂CON(CH₃)₂ containing a peptide bond are prepared for the synthesis of DNICs with/without intra-molecular hydrogen bonding, respectively. The IR ν(NO) bands of [(NO)₂Fe(SCH₂CONHCH₃)₂]⁻ (2) appears at 1751, 1700 cm⁻¹. In complex 2, the presence of intramolecular [NH?S] hydrogen bonding was verified by the observation of IR spectroscopy with N−H stretching frequency 3334 cm⁻¹ (CDCl₃) and subsequently confirmed by single-crystal X-ray diffraction showing N−S distance of 2.94 Å. Complex 2 displays the rhombic EPR spectrum with g₁ = 2.039, g₂ = 2.031 and g₃ = 2.013 at in frozen H₂O. Complexes 2 and 3 rapidly release NO when exposed to light. The time needed for photolysis reactions of 2 is two times faster than that of 3 in less polar solvent. Representative time courses for the photolability of 2 and 3 in THF display the NO-off ability: 2 > 3.     

Hydrogen abstraction from neurotransmitters by active oxygen species facilitated by intramolecular hydrogen bonding in the radical intermediates

The reactivity of neurotransmitters toward hydrogen abstraction by an active oxygen species (the cumylperoxyl radical) is comparable to that of a strong antioxidant such as catechin due to the strong intramolecular hydrogen bonding, which has been successfully detected by ESR.     

Oligo(p-phenylene-ethynylene)s with backbone conformation controlled by competitive intramolecular hydrogen bonds

A series of conjugated oligo(p-phenylene-ethynylene) (OPE) molecules with backbone conformations (that is, the relative orientations of the contained phenylene units) controlled by competitive intramolecular hydrogen bonds to be either co-planar or random were synthesised and studied. In these oligomers, carboxylate and amido substituents were attached to alternate phenylene units in the OPE backbone. These functional groups were able to form intramolecular hydrogen bonds between neighbouring phenylene units. Thereby, all phenylene units in the backbone were confined in a co-planar conformation. This planarised structure featured a more extended effective conjugation length than that of regular OPEs with phenylene units adopting random orientation due to a low rotational-energy barrier. However, if a tri(ethylene glycol) (Tg) side chain was appended to the amido group, it enabled another type of intramolecular hydrogen bond, formed by the Tg chain folding back and the contained ether oxygen atom competing with the ester carbonyl group as the hydrogen-bond acceptor. The outcome of this competition was proven to depend on the length of the alkylene linker joining the ether oxygen atom to the amido group. Specifically, if the Tg chain folded back to form a five-membered cyclic structure, this hydrogen-bonding motif was sufficiently robust to overrule the hydrogen bonds between adjacent phenylene units. Consequently, the oligomers assumed non-planar conformations. However, if the side chain formed a six-membered ring by hydrogen bonding with the amido NH group, such a motif was much less stable and yielded in the competition with the ester carbonyl group from the adjacent phenylene unit. Thus, the hydrogen bonds between the phenylene units remained, and the co-planar conformation was manifested. In our system, the hydrogen bonds formed by the back-folded Tg chain and amido NH group relied on a single oxygen atom as the hydrogen-bond acceptor. The additional oxygen atoms in the Tg chain made a negligible contribution. A bifurcated hydrogen-bond motif was unimportant. From our results, in combination with the results from an independent study by Meijer et al., it is evident that intramolecular hydrogen bonds involving back-folded oligo(ethylene glycol) moieties may differ in their structural details. Absorption spectroscopy served as a convenient yet sensitive technique for analysing hydrogen-bonding motifs in our study.     

Synthesis and intramolecular hydrogen bonding networks of 2,4,6-tri(o-hydroxyaryl)-1,3,5-triazines

Functionalized, triaryl substituted triazines were synthesized via the Friedel-Crafts arylation reaction. These conjugated triazines possess unique, intramolecular hydrogen bonding motifs, which provide tunable planarity.     

NMR-spectroscopic study of conjugation effects. 9.13C NMR spectra of alkyl vinyl sulfoxides and sulfones

Conclusions Polarization and steric effects of the alkylhetero groups have the main influence on the C^1,2 chemical shifts of the vinyl fragment in alkyl vinyl sulfoxides and sulfones. In sulfones, an appreciable role can be played by a -acceptor interaction between the sulfur atom and the double bond.For the previous communication, see [I].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1007–1011, May, 1980.     

Macrocyclization of alpha-(alkynyloxy)silyl-alpha-diazoacetates by inter-/intramolecular

Thermally induced intra-/intermolecular [3 + 2] cycloaddition reaction sequences of alpha-(alkynyloxy)silyl-alpha-diazoacetates 1 lead to [3.3](1,4)pyrazolophanes (2)2 and higher cyclooligomers thereof [(2)n, n > 2]. In most cases, the cyclodimer was isolated by crystallization, while a complete separation of the mixture of the higher cyclooligomers was not possible. Solid state structures of cyclodimers (2b)2 and (2c)2, cyclotrimer (2b)3, and cyclotetramer (2e)4 were determined by X-ray diffraction analysis. Field-desorption mass spectra were used to characterize the cyclooligomer mixtures. The relative amounts of the cyclooligomers depend on the substitution pattern of the diazo compound. The cyclooligomerization reactions reported herein demonstrate, for the first time, the involvement of diazo functions in macrocyclization reactions via 1,3-dipolar cycloaddition.     

Viscometric investigation of intramolecular hydrogen bonding cohesional entanglement in extremely dilute aqueous solution of poly vinyl alcohol

An investigation of influence of cryogenic treatment on extremely dilute aqueous solution of poly(vinyl alcohol) (PVA) was performed by viscometry. The solution was frozen in liquid nitrogen or in a freezer at −25°C, then thawed at ambient temperature and concentrated by evacuation. The viscosity of the solution was measured using the dilute method. The experimental results indicated that the viscosity of the solution is related to N, the times of the freezing and thawing cycle, and the temperature for freezing. Undergoing a treatment of freezing and thawing, the viscosity of the solution is decreased, while it can be recovered the value of before the treatment as the solution had been heated at a high temperature. Thus, a conclusion may be obtained; that is, for an extremely dilute aqueous solution of PVA, which concentration is below C_gel, threshold concentration for gelation, an intramolecular hydrogen bonding cohesional entanglement can be formed by freezing as N < 5. However, in the case of N > 5, it not only formed an intramolecular hydrogen bonding but also produced an intermolecular hydrogen bonding. At the same time, the abnormal behavior of reduced viscosity of the solution in extremely dilute concentration region has been explained. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2421–2427, 1997     

1H NMR studies of intramolecular hydrogen bonding in N-(pyridyl)amides of 6-methylpicolinic acid N-oxide

The ¹H NMR spectra of seven N-(pyridyl)amides of 6-methylpicolinic acid N-oxide in chloroform were obtained. The influence on the chemical shifts of the N? H protons of temperature, concentration and the CH₃ substituent in the pyridine ring was studied. The N? H protons were found to be shifted to low fields (～14 ppm) owing to the formation of strong intramolecular hydrogen bonding. The influence of the pyridine ring on the chemical shift of the N? H proton is comparable with the inductive effect of the p-nitrophenyl group. The hindered rotation around the N-pyridyl bond of N-(α-pyridyl)amides of 6-methylpicolinic acid in solution is discussed.     

VT 1H NMR investigations of resonance-assisted intramolecular hydrogen bonding in 4-(dimethylamino)-2'-hydroxychalcone

[reaction: see text] Resonance-assisted intramolecular hydrogen bonding in both polar aprotic and nonpolar solutions of 4-(dimethylamino)-2'-hydroxychalcone (DMAHC) has been investigated by variable-temperature proton NMR spectroscopy. In both nonpolar and polar solvents, the signal for the phenolic hydrogen moves downfield as the temperature is lowered. In each solvent system studied, a linear relationship between chemical shift and temperature was observed.     

Control of structure and photophysical properties by protonation and subsequent intramolecular hydrogen bonding

Protonation and subsequent intramolecular hydrogen bonding as methods to control chain structure and tune luminescence in heteroatomic conjugated polymers were reported experimentally [A. P. Monkman et al., J. Am. Chem. Soc. 124, 6049 (2002)]. In this paper, the structure and photophysical properties of the model teraryl compound of phenylene-pyridylene copolymer before and after protonation are theoretically studied with quantum chemistry methods. From the optimized ground states, intramolecular hydrogen bonding to the adjacent oxygen atom in the alkoxy substituent planarizes the backbone of the molecules, and the optimized detailed results of compound 9 before and after protonation, such as the dihedral angles between the central benzene and the two pyridyl rings, the bond lengths, and the bond angles, are consistent with the experimental results. From the results of the calculated excited states, the protonation and subsequent intramolecular hydrogen bonding result in the redshifts of the absorption, the increase of the ionization energy, the increase of the electron affinity, the decrease of the energy difference of the highest occupied molecular orbital and lowest unoccupied molecular orbital, the decrease of the binding gap, and the delocalization of the electron-hole coherence. The photophysical properties of compound 9 before and after protonation are further studied with a three-dimensional real-space analysis method of transition and charge difference densities (study transition dipole moment and charge transfer in the absorption and fluorescence processes) and two-dimensional real-space analysis method of transition density matrices (study the electron-hole coherence and the excitation delocalization). The calculated results show theoretically an insight understanding on the influence of the protonation and subsequent intramolecular hydrogen bonding to chain structure and photophysical properties.     

Oxidation of sulfoxides by hydrogen peroxide,catalyzed by methyltrioxorhenium(VII)

Dialkyl and diaryl sulfoxides are oxidized to sulfones by hydrogen peroxide using methyltrioxorhenium as the catalyst. The reaction rate is negligible without a catalyst. The kinetics study was performed in CH3CN-H2O (4:1 v/v) at 298 K with [H+] at 0.1 M, conditions which make the equilibration between MTO and its peroxo complexes more rapid than the oxygen-transfer step. The values for the rate constant for the oxygen-transfer step lie in the range 0.1-3 L mol-1 s-1. The rate constants were significantly smaller than for the oxidation of sulfides to sulfoxides. A study of ring-substituted diaryl sulfoxides yielded kinetics results that are consistent with nucleophilic attack of the sulfur atom on the peroxide oxygen group since rho = -0.65. The results cited refer to the reactions of the diperoxo from the catalyst, MeRe(O)(eta 2-O2)2H2O. The monoperoxo complex showed no measurable reactivity toward sulfoxides, in contrast with the situation for nearly every other substrate. That unusual finding suggests a hydrogen-bonded interaction between the substrate and the diperoxorhenium compound which cannot exist with the monoperoxo compound.