On the bond order of C2 and N2

The commonly adopted bond order values of C₂ and N₂ are critically investigated with a new bond order concept. Ab initio calculations with extended basis sets suggest that C₂ can be described by a double to triple bond closer to acetylene than to ethylene and N₂ by a triple bond. The basis set dependence is discussed. Also a relation between the number of basis functions, MO's and non-vanishing eigenvalues of the bond order parts of the density matrix is presented.     

Stereospecific synthesis of a dl-gala-aminoquercitol derivative

A new aminoquercitol derivative was synthesized starting from 1,4-cyclohexadiene. Photooxygenation of cyclohexa-1,4-diene afforded anti-2,3-dioxabicyclo[2.2.2]oct-7-en-5-yl hydroperoxide as the main product. The formed hydroperoxy endoperoxide was reduced with LiAlH₄ to produce anti-2,3-dioxabicyclo[2.2.2]oct-7-en-5-ol. Protection of alcohol with acetyl chloride followed by reduction of the endoperoxide with thiourea, and then palladium-catalyzed ionization/cyclization reaction gave an oxazolidinone derivative. Hydrolysis of the oxazolidinone ring and acetylation gave an amino compound. Oxidation of the double bond in the amino compound with OsO₄ followed by acetylation gave the amino tetraacetate and removal of the acetate groups furnished the desired aminoquercitol whose exact configuration was determined by X-ray diffraction analysis.     

Vapor phase hydrofluorination of acetylene to vinyl fluoride over La2O3-Al2O3 catalysts

A series of La-doped Al₂O₃ catalysts were prepared and tested for the vapor phase hydrofluorination of C₂H₂ to vinyl fluoride (CH₂CHF, VF). It was found that the La-doped catalyst gave a stable catalytic performance and a higher selectivity to the desired VF and a lower selectivity to coke deposition compared with the pure Al₂O₃ catalyst. The enhancement in VF selectivity on the La-doped catalyst was due to the elimination of acidic sites on the Al₂O₃ surface by the addition of La₂O₃, evidenced by NH₃-TPD results, which could also explain the declined selectivity to coke deposition on the catalyst. Raman result indicated there were two different vibration forms of CH distortion and CC expansion for the coke deposition.     

Synthesis of eight-membered aminocyclitol analogues

The first syntheses of four stereoisomeric diaminocyclooctane diols, as well as a chlorocyclooctane aminodiol, are reported. In the first part, photooxygenation of cis,cis-1,3-cyclooctadiene gave a bicyclic endoperoxide, which was reduced with zinc followed by mesylation of the hydroxyl groups. Treatment with sodium azide afforded 1,4- and 1,2-cyclooctene diazides. Oxidation of the double bonds in the isomeric diazides with OsO₄, followed by hydrogenation of the azide groups, led to 3,8-diaminocyclooctane-1,2-diol and 3,4-diaminocyclooctane-1,2-diols. In the second part, cis-3,8-diazidocyclooctene was converted into the corresponding epoxide. Stereospecific hydrolysis of the epoxide ring with HCl_(g) in methanol, and hydrogenation of the azide groups gave 3,8-diamino-2-chloro-cyclooctan-1-ol. Bromination of the double bond in cyclooctene diacetate, followed by acetate deprotection, azidolysis of the bromides, and hydrogenation of the azide groups resulted in the formation of 2,3-diaminocyclooctane-1,4-diol.     

Stability of functionalized C60 paramagnetic dimers and monomers

Density functional theory is used to calculate the bond dissociation energy to cleave the C₆₀C₆₀ bond of the paramagnetic X-C₆₀C₆₀-X and X-C₆₀C₆₀ dimers where X is F, OH, O and H. The results show that these dimers would not be stable much above room temperature and therefore cannot constitute the paramagnetic phase needed to form the observed ferromagnetism which has been shown to be stable up to 800 K. The calculated bond dissociation energies to remove an F, OH or H from a single C₆₀ are large suggesting that they could be the source of the unpaired spin needed for the high temperature ferromagnetism.     

Investigations on the local angular distortions and the spin-Hamiltonian parameters for Ni in sulfides

The local angular distortions and the spin-Hamiltonian parameters (the g factors and the hyperfine parameters) for Ni⁺ in ABS₂ (ACu, Ag; BAl, Ga) ternary sulfides are theoretically investigated from the perturbation formulas of these parameters for 3d⁹ ions in a tetragonally distorted tetrahedron. In view of the strong covalency of such systems, the ligand orbital and spin–orbit coupling contributions are taken into account using the cluster approach. The local impurity-ligand bond angles in the Ni⁺ centers are found to be about 1.4–4.5° smaller than those of the host monovalent A sites in the pure crystals, due to size mismatching substitution. As a result, the ligand tetrahedra exhibit slight elongation in CuBS₂:Ni⁺ and slight compression in AgGaS₂:Ni⁺. The calculated spin-Hamiltonian parameters, optical transitions and the relative intensity ratios show reasonable agreement with the experimental data.     

Metalation reactions—VIII Metalation of 1,4-enynes and protonation of their anions

A series of 1,4-enynes was prepared and the compounds metalated with butyllithium in ether. The formation of the mono- and dilithio derivatives was studied by PMR and UV. Protonation of the dilithio compounds gave vinylallenes, 1,3- and 1,4-enynes. Isomerisation of the 1,4-enynes in DMSO using dimsylsodium gave vinylacetylenes from compounds containing a terminal double bond and vinylallenes from those with an internal double bond. The sequence of the H—D exchange of the various protons was also studied.     

Reductive aldol-type reaction of α,β-unsaturated esters with aldehydes or ketones in the presence of Rh catalyst and Et2Zn

The reaction of RhCl(PPh₃)₃ with Et₂Zn easily generated a rhodium–hydride complex (Rh−H) that added to α,β-unsaturated esters to form rhodium enolate complexes by formal 1,4-reduction. These rhodium enolates gave the corresponding Reformatsky-type reagents through transmetalation, and they reacted with various aldehydes and ketones to give reductive aldol-type products in good to excellent yields.     

Rh2(OAc)4-catalyzed reaction of 1,3-dioxanes with methyl diazoacetate

The reactions of methyl diazoacetate with 1,3-dioxanes in the presence of Rh₂(OAc)₄ afford 1,4-dioxepanes in up to 46% yields. The insertion of methoxycarbonylcarbene into the C—O bond occurs only in the case of 2-phenyl-1,3-dioxanes.     

Synthesis and Characterization of Novel Aryl Cyclitols: Polycyclitols

New polycyclitols were synthesized starting from 1,4-naphthoquinone. An endo-selective Diels–Alder cycloaddition between 1,4-naphthoquinone and 1-acetoxybutadiene afforded a diketone. Reduction of the diketone with a NaBH₄-CeCl₃ · 7H₂O system gave a new cyclitol analog diol acetate. Acetylation of this compound afforded a triacetate. Oxidation of the double bond of the triacetate compound with OsO₄ followed by acetylation of hydroxyl groups gave the pentaacetate, whose structure was established unequivocally via application of x-ray crystallographic methods. Hydrolysis of ester groups of pentaacetate under basic condutions furnished the desired and another novel aryl cyclitol.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource: Full experimental and spectral details.]     

On the Reactivity of Phosphaalumenes towards C−C Multiple Bonds

Heterocycles containing group 13 and 15 elements such as borazines are an integral part of organic, biomedical and materials chemistry. Surprisingly, heterocycles containing P and Al are rare. We have now utilized phosphaalumenes in reactions with alkynes, alkenes and conjugated double bond systems. With sterically demanding alkynes 1,2-phosphaalumetes were afforded, whereas the reaction with HCCH or HCCSiMe₃ gave 1,4-phosphaaluminabarrelenes. Using styrene saturated 1,2-phosphaalumates were formed, which reacted further with additional styrene to give different regio-isomers of 1,4-aluminaphosphorinanes. Using ethylene, a 1,4-aluminaphosphorinane is obtained, while with 1,3-butadiene a bicyclic system containing an aluminacyclopentane and a phosphirane unit was synthesized. The experimental work is supported by theoretical studies to shed light on the mechanism governing the formation of these heterocycles.     

PhI(OAc)2 and BF3–OEt2 mediated heterocyclization: metal-free synthesis of pyrimidine-annulated oxazolines

A simple high yielding and highly efficient synthesis of oxazoline ring fused with uracil moiety is reported. Hypervalent iodine (PIDA) in the presence of BF₃–OEt₂ generates an effective electrophile to activate uracil C5–C6 double bond leading to heterocyclization.     

Regio- and Diastereoselective Michael Additions by Unsymmetrical Allylic Anions Upon Ethyl Propiolate

A convenient and efficient procedure for regio- and diastereoselective addition of prenyl and geranyl anions to ethyl propiolate is reported. This 1,4-addition reaction produces exclusively the trans isomer at the double bond deriving from the triple bond of ethyl propiolate without rearrangement of the starting primary, allylic carbanion nucleophile.     

A phosphoryl to spiro-bicyclophosphorane transformation via β-amidic proton elimination in phosphorylated hydrazides

The reaction between phosphoryl-containing reagents and hydrazides has been studied. The tetrahedral phosphoryl structure is transformed into a spiro-bicyclophosphorane system with trigonal bipyramidal geometry by the elimination of a β-amidic proton in the reaction between a hydrazide and phosphoryl reagents with at least two leaving groups (Cl) bound to the phosphorus atom, such as POCl₃ or PhPOCl₂. In the spiro-bicyclophosphorane structure, the CN imine bond is formed upon β-amidic proton elimination, leading to the conversion of the CO into a C-O bond and the formation of a P-O bond. All of these structural rearrangements are supported by X-ray crystallography data, and NMR and IR experiments.     

The Effects of Intramolecular Hydrogen Bonding on the Reaction of Phenols with Epoxide in the Presence of Nano Calcium Carbonate

The reaction of phenols and dihydroxybenzenes with epoxide in the presence of nano CaCO₃ was studied. Catechol could react with epoxide and gave monochlorohydrin derivative; other dihydroxybenzenes and monomeric phenols had no reaction under the same conditions. The reaction of catechol with epoxide did not occur when nano CaCO₃ was replaced by a normal one. These were attributed to the strong interaction between nano CaCO₃ and the substrate as catechol possessed intrahydrogen bond and excess active hydrogen, which can induce the intramolecular proton transfer via the intramolecular hydrogen bond and promote the reaction of hydroxyl and epoxide. This is an example revealing the unique role of the hydrogen bond played in chemical reactions.     

Design, synthesis, and structural aspects of chalcogen-substituted pyridine dicarboxamide donors and their reactions

The design and synthesis of a new family of potentially pentadentate N₃Se₂ or N₃Te₂ type donors bearing a 2,6-disubstituted pyridine dicarboxamide moiety as the central fragment [-NH-C(O)-pyridine-C(O)-NH-] functionalized with chalcogen as additional donors in the appended arms of the pyridine ring through the alkyl spacers and their potential applications and reactivity toward d⁸ and d¹⁰ metal ions have been demonstrated.     

Synthetic transformations of higher terpenoids: XXV. Cross coupling of phlomisoic acid methyl ester with alkenes in the presence of oxidants

The reaction of phlomisoic acid methyl ester with styrene, catalyzed by Pd(OAc)₂, in the presence of Cu(OAc)₂ and 1,4-benzoquinone in a mixture of propionic acid with diethyl ether gave the corresponding 15,16-distyryl derivative and only traces of 15- and 16-monosubstituted furanolabdanoids. Oxidative coupling of the title compound with methyl acrylate under analogous conditions afforded a mixture of 15-mono-, 16-mono-, and 15,16-dialkenylation products whose ratio changed during the process. The reaction was stereoselective, and the exocyclic double bond in the products had exclusively E configuration.     

Reaction of metal-Carbene complexes with vinyllithium reagents

The reaction of vinyllithium with (CO)₅CrC(OCH₃)C₆H₅ (Ic) at?78° followed by the treatment with HCl at ?78° gave 43% (Z)-1-methoxy-1-phenylpropene (IIIa) and 21% 1,4-dimethoxy-1,4-diphenyl-1,3-butadiene (IVa) and no trace of a vinylphenylcarbene complex or its expected decomposition products. IIIa and IVa are proposed to arise from electrophilic attack at the carbon-carbon double bond of a σ-allychromium intermediate. The reaction of phenyllithium with (CO)₅CrC(OCH₃)CH=CHC₆H₅ (V) gave 9% (CO)₅CrC(OCH₃)CH₂CH- (C₆H₅)₂(VI) and 17% (E)-1-methoxy-1,3-diphenylpropene (VII). Reaction of V with lithium diphenylcuprate gave 30% of the conjugate addition product VI.