The manipulation of the enone moiety associated with the biomass-derived, homochiral and now abundant compound levoglucosenone (1) is described. While the trichloroacetimidates derived from the allylic alcohols 3 and 4 failed to engage in Overman-type rearrangements, certain ester derivatives reacted in the presence of Pd[0]-catalysts to give regio-isomeric mixtures of β,γ-unsaturated malonates or ketones, the structures of which were confirmed by single-crystal X-ray analyses. In other sequences involving 1,3-transposition reactions, an operationally simple means for converting compound 1 into isolevoglucosenone (2) is described.
A three‐step transformation consisting of 1) addition of electrochemically generated iodosulfonium ions to vinylarenes to give (1‐aryl‐2‐iodoethoxy)sulfonium ions, 2) nucleophilic substitution by subsequently added aromatic compounds to give 1,1‐diaryl‐2‐iodoethane, and 3) elimination of HI with a base to give 1,1‐diarylethenes was developed. The transformation serves as a powerful metal‐ and chemical‐oxidant‐free method for alkenyl C?H/aromatic C?H cross‐coupling. 相似文献
Solid-state scintillating materials were synthesized by the co-doping of sol–gel components with neutron absorbers [6Li and 10B], organic fluorescence sensitizers such as salicylic acid and 2,5-diphenyloxazole (PPO) and activator 1,4-bis-2-(5-phenyloxazolyl)-benzene (POPOP). The room-temperature sol–gel process through the addition of organic polymers is the key to the successful entrapment of the organic sensitizers and activator in inorganic matrixes. These transparent or translucent sol–gel scintillators were evaluated for alpha radiation and neutron detections. 相似文献
Several O-and N-linked inositols and/or aminoinositols have been prepared by iterative opening of epoxides and aziridines derived from homochiral cyclohexadiene cis-diols. The three inositols and their intermediate conduritols (conduramines) were tested against several glycosidases (alpha- and beta-glucosidase, alpha- and beta-galactosidase, alpha- and beta-mannosidase) in an assay that measured the rate of hydrolysis of p-nitrophenolglycosides rather than the concentration of p-nitrophenolate. Somewhat surprisingly, the best inhibition was seen against beta-galactosidase with several of the compounds. The inositols linked through oxygen or nitrogen were subjected to calcium binding studies performed in NMR experiments. Detailed analysis of the title compounds by NMR spectroscopy has been performed, and full assignments were made. One of the attendant benefits of the preparation of these compounds has been expressed in the design and synthesis of new salen catalysts whose effectiveness has been compared with Jacobsen's catalyst in the epoxidation of styrene. 相似文献
Trapping intermediates on the Prins cyclisation pathway with carbon-based nucleophiles has given further insight into factors affecting the acid-mediated reactions of homoallylic alcohols with aldehydes, enabling the design of efficient syntheses of 4-hydroxy-2,6-disubstituted tetrahydropyrans. 相似文献
The stereochemical outcome of the intramolecular Diels-Alder reaction of ester-linked 1,3,8-nonatrienes can be controlled by substituents about a stereogenic center attached to C1. The scope and limitations of this approach have been investigated, with variation in substrate structure about the allylic stereocenter and the dienophile. The stereochemical outcomes of these reactions are explained by reference to B3 LYP/6-31G(d) transition structures. New insights into the conformational preferences of allylic alcohol derivatives are reported, results which allow an explanation of the differing levels of pi-diastereofacial selectivity and cis/trans (i.e. endo/exo) selectivity from the reaction. 相似文献
In this paper we generalize our previous work on the use of time-dependent projection operators for the derivation of master equations for general systems. Previously we had generalized the usual time-independent projection operator approach to include time-dependent projection operators, in which the relevant part of the full density operator is considered to be the uncorrelated part of the full density operator. The irrelevant part of the density operator was then the part describing the correlations between the coupled systems. In the present work we present new time-dependent projections operators which have the property that some correlations between the interacting subsystems are placed in the relevant part of the distribution function and the remaining correlations are placed in the irrelevant part of the distribution function. 相似文献
Ab initio computational, microwave spectroscopic, and electron diffraction techniques have been used to study the gas-phase structure of cyclopropylbenzene. Theoretical calculations at the HF, B3LYP, and MP2 levels for basis sets 6-31G(d) and 6-311G(d) have been carried out. Both MP2 and B3LYP calculations showed the bisected form to be lower in energy (245/157 and 660/985 cal mol(-1), respectively, for basis sets 6-311G(d)/6-31G(d)). Rotational constants for the bisected form of the parent and eight singly substituted (13)C isotopic species were obtained. The selection rules of the observed rotational transitions and the facts that eight (rather than six) singly substituted (13)C isotopers are observed and assigned and that seven of the compound's nine carbon atoms lie in the molecule's symmetry plane required the molecule to exist in the bisected conformation. No transition from the perpendicular form was observed in the pulsed-jet microwave experiment. Gas-phase electron diffraction data were collected at a nozzle-tip temperature of 265 K. Least squares analyses were carried out using ED data alone and with the inclusion of microwave rotational constants. The principal structural results (r(g) and angle(alpha)) obtained from the combined ED/MW least-squares analysis are r(C-H)(av) = 1.093(6) A, r(C(7)-C(8))(v) = 1.514(20) A, r(C(8)-C(9))(d) = 1.507(26) A, r(C(7)-C(1)) = 1.520(25) A, r(C-C)(Ph) = 1.395(1) A, angleC(1)C(7)C(8) = 119.6(17) degrees, angleC(2)C(1)C(7) = 122.5(25) degrees, angleC(1)C(2)C(3) = 120.9(35) degrees, angleHC(8)C(9) = 116.7(20) degrees, angleHCC(Ph) = 120.0 degrees (assumed). 相似文献