A quantitative analysis of the through-space and the through-bond interactions between lone-pairs in azines: pyridazine,pyrimidine and pyrazine

The INDO calculations were performed on the three azines: pyridazine, pyrimidine, and pyrazine. The cannonical molecular orbitais obtained by these calculations were then transformed into the localized molecular orbitals. With the use of the localized molecular orbitals, the variation in the lone-pair orbital energies of these molecules were pursued in the light of the through-space and/or the through-bond interactions between the specified localized molecular orbitals in a molecule selectively. The interactions were expressed by the summation of several terms: through-space, through-bond, through-virtuals and coupling terms.     

A practical asymmetric synthesis of trans-4,5-benzhydrindan-1-ones as a precursor of A-nor B-aromatic steroidal compounds

The enantio-controlled synthesis of trans-4,5-benzhydrindan-1-ones was achieved by means of a stereoselective [4+2] cycloaddition of o-quinodimethanes generated by a thermal cleavage of benzocyclobutene derivatives as a key step. The chiral substrates of the thermal reaction were synthesized by a diastereoselective Grignard addition to the chiral O-isopropylideneglyceroketones connected to a benzocyclobutene ring, which were simply prepared from D-mannitol as a chiral source. This approach can provide a new efficient access to A-nor B-aromatic steroidal compounds.     

Additive telluromolybdates. Structure and catalysis in oxidation

Additive telluromolybdates, MoO₃·2TeO₂ and M^IIO·TeO₂·MoO₃ (M^IITeMoO₆; M^II = Co, Mn, Zn), converted ethyl lactate selectively to pyruvate in a vaporphase fixedbed flow system at 250–300 °C. A synergy in activity was observed for binary TeO₂–MoO₃, and crystalline Te₂MoO₇ was suggested as the active species. The Rietveld analysis of powder XRD patterns of ternary CoTeMoO₆ revealed the layer structure quite different from that of the reference Te₂MoO₇, but tellurium was again located adjacent to molybdenum linked through lattice oxygen.     

Vibrational spectra and molecular conformations of 1,5-dichloro- and 1,5-dibromopentanes and 1,6-dichloro-and 1,6-dibromohexanes

The Raman and IR spectra of 1,5-dichloro- and 1,5-dibromopentanes and 1,6-dichloro-and 1,6-dibromohexanes have been measured. The normal coordinates have been calculated for these molecules using a consistent set of force constants and the molecular conformations studied by analysing the spectra with reference to the results of the calculations. In the crystalline solid state, 1,5-dichloropentane assumes the trans-trans-trans-gauche form and 1,5-dibromopentane, 1,6-dichloro- and 1,6-dibromohexanes assume the all-trans form. The normal coordinate treatment with the well-established force field was of great help in determining the whole molecular form of the relatively large chain molecules.     

Cidep study of radical-ion pair systems: Photooxidation reactions of carbazoles by maleic anhydride in alcohol solution

Photooxidation (charge transfer) reactions of carbazole derivatives by maleic anhydride (MA) in alcoholic media are studied by a time-resolved cw-ESR (TRESR) and Fourier transform ESR (FTESR) techniques. The CIDEP spectra observed in the systems (methyl-, ethyl-, and phenyl-substituted carbazoles with MA) remarkably depend on the MA concentration. Under the high concentration conditions, an emissive TM (triplet mechanism) polarization with a slight A/E (absorption/emission) pattern of the RPM (radical pair mechanism) is observed. In the low concentration of MA, a TM-like absorptive polarization is superimposed on the A/E pattern of the RPM. Since this reaction takes place exclusively through the triplet state, this spectral phase reveals that the singlet state of the radical-ion pair (RIP) has an energy higher than that of the triplet state, in other words, the sign of the apparent exchange interaction of the present RIP systems is positive. The total absorptive polarization observed in the low concentration of MA is tentatively explained by the polarization transfer from the excited triplet state of carbazoles in thermal equilibrium.     

Polymeric organosilicon systems. XVII. Synthesis and photochemical and conducting properties of poly[o-and m-(disilanylene)phenylene]s

Poly[o-(tetramethyldisilanylene)phenylene] ( 2a ), poly[o-(1,2-dimethyldiphenyldisilanylene)-phenylene] ( 2b ), poly[m-(tetramethyldisilanylene)phenylene] ( 2c ), and poly[m-(1,2-dimethyldiphenyldisilanylene)phenylene] ( 2d ) were prepared by the sodium condensation reaction of the corresponding 1,2-and 1,3-bis (chlorosilyl)benzenes in toluene. Irradiation of thin films of 2a-2d in air resulted in a rapid decrease of absorption maxima in the ultraviolet region. The photolysis of 2b and 2d in benzene afforded photodegradation products with low molecular weights. When thin films of 2b and 2d were doped with antimony pentafluoride vapor, films which have conductivities of semi-conductor level were obtained. © 1993 John Wiley & Sons, Inc.     

Highly (Z)-selective synthesis of beta-monosubstituted alpha,beta-unsaturated cyanides using the peterson reaction

[reaction: see text] The Peterson reaction between (t-BuO)Ph(2)SiCH(2)CN and various aldehydes furnishes the corresponding beta-monosubstituted alpha,beta-unsaturated cyanides with high Z selectivity (Z:E = 92:8 to >98:2).     

Ruthenium-catalyzed carbonylative cycloaddition of alpha-keto lactones with alkenes or alkynes: the participation of an ester-carbonyl group in cycloaddition reactions as the two-atom assembling unit

The reaction of benzofuran-2,3-dione derivatives 1 with CO and alkenes (or alkynes) results in a carbonylative [2+2+1] cycloaddition in which the ester-carbonyl group is incorporated into a two-atom assembling unit to give spirolactone derivatives 2. This reaction provides the first example of an ester-carbonyl group participating in a carbonylative cycloaddition reaction.     

Ruthenium-catalyzed reaction of alpha,beta-unsaturated imines with carbon monoxide and alkenes leading to beta,gamma-unsaturated gamma-butyrolactams: involvement of direct carbonylation at olefinic C[bond]H Bonds as a key step

The reaction of alpha,beta-unsaturated imines with CO and alkenes in the presence of Ru(3)(CO)(12) as a catalyst results in a three-component coupling reaction that gives alpha,alpha-disubstituted beta,gamma-unsaturated gamma-butyrolactams. The reaction proceeds via a two-step sequence involving the initial formation of ketone derivatives by catalytic carbonylation at the beta-olefinic C-H bonds of alpha,beta-unsaturated imines, followed by the (uncatalyzed) intramolecular nucleophilic attack of the imine nitrogen on the ketonic carbon to generate a tetrahedral intermediate, which then undergoes a 1,2-ethyl migration. The reaction of a cyclic unsaturated imine, derived from the reaction of (1R)-(-)-myrtenal with tert-butylamine, gives a beta-aminocyclopentene derivative, which is formed by an aldol-type condensation of the initially formed ketone, indicating the initial formation of ethyl ketone.