Search results for "Reaction"
showing 10 items of 6134 documents
Photochemical generation of benzene–naphthalene biplanemers
2005
Abstract A direct biplanemer synthesis could be achieved by a quantitative [4π+4π]photocycloaddition of benzyloxy substituted benzene and naphthalene rings ( 3d , e ⇄ 4d , e ). Since the products do not show a thermal Cope rearrangement—in contrast to the related longicyclic conjugated 9,10-benzotricyclo[4.2.2.2 2,5 ]dodeca-3,7,9-trienes—but a quantitative reverse reaction, they are interesting systems for an optical switching.
Influence of Reactant Polarity on the Course of the Inverse-Electron-Demand Diels−Alder Reaction. A DFT Study of Regio- and Stereoselectivity, Presen…
1999
The molecular mechanisms for the inverse-electron-demand Diels−Alder reactions between nitroethene and three substituted ethenes (propene, methyl vinyl ether, and dimethylvinylamine) to give the corresponding nitroso cycloadducts have been characterized with density functional theory methods using the B3LYP/6-31G* calculational level. On the basis of stability arguments and molecular orbital analysis relative rates, regioselectivity, and stereoselectivity, the presence of Lewis acid catalyst modeled by the BH3 system and the inclusion of solvent effects as a function of the nature of substituent in the dienophile fragment are analyzed and discussed. The ortho attack mode presents transition…
First synthesis of chiral 3-vinylindoles as 4π-components for diels-alder reactions
1995
The first syntheses of chiral 3- and 2-vinylindoles bearing sulfoxide or (-)-menthyloxy functional groups at the β-vinyl positions by way of procedures based on the Horner-Wadsworth-Emmons and Wittig reactions, respectively, are described. Some Diels-Alder reactions demonstrating the 4π-reactivity of these compounds are reported.
Synthesis, Characterisation, and Reactivity of 1-(1-Methylimidazol-2-yl)ethenes
1990
Abstract Thermally labile 1-(1-methylimidazol-2-yl)-ethenes, synthesised using the Wittig reaction, have been characterised as stable picrate or N-phenacyl salts. The free bases can be regenerated from the picrates on treatment with triethylamine and their reactivity with dienophiles is described.
Organolanthanides as single component homogeneous catalysts for isoprenehex—1-ene co-polymerisation
1999
Abstract Bisallylansalanthanide complexes act as single component catalysts of diene polymerisation; from an equimolar mixture of isoprene and hex-1-ene, a co-polymer hex-1-ene/isoprene = 1:10 is obtained, this copolymer is essentially formed of 1,4- trans polyisoprene blocks separated by only one inserted hexyl group.
2,2′-Dimethyl-2,2′-(m-phenylenedimethylene)propanedinitrile
2009
The title compound, C16H14N4, features an aromatic ring with two 2,2´-dicyanopropyl residues in positions 1 and 3, which are located above and below the ring plane. The two residues differ in their conformation with respect to the aromatic ring: whereas one of the Cmethyl-C-Cmethylene-Caromatic torsion angles is gauche [68.93 (12)°], the other one is fully staggered [177.63 (9)°]. The crystal structure is stabilized by C-H...N hydrogen-bonding interactions. Key indicators: single-crystal X-ray study; T = 173 K; mean σ(C–C) = 0.002 Å; R factor = 0.037; wR factor = 0.101; data-to-parameter ratio = 15.0.
Highly Enantio- and Diastereoselective Inverse Electron Demand Hetero-Diels-Alder Reaction using 2-Alkenoylpyridine N-Oxides as Oxo-Heterodienes
2008
A general catalytic inverse electron demand hetero-Diels Alder reaction for 2-alkenoylpyridine N-oxides is presented. 2-Alkenoylpyridine N-oxides react very efficiently with alkenes in the presence of bisoxazolidine-copper(II) [BOX-Cu(II)] complexes to give chiral dihydropyrans bearing a pyridine ring at the 6-position with very high yields and excellent diastereo- and enantioselectivity. These heterodienes exhibited higher reactivity and enantioselectivity than the corresponding non-oxidized 2-alkenoylpyridines.
ChemInform Abstract: Synthesis of Tripyreno[2,3,4,-abc:2,3,4-ghi:2,3,4-mno][18]annulenes.
2001
The title compounds were prepared in a multi-step synthesis in which primarily the pyrene building blocks were formed (1,2 11a,b). The final reaction step 11a,b 12a,b consisted of a threefold trans selective cyclocondensation process that generated the central 18-membered ring. Hexyloxy or dodecyloxy sidechains attached on the periphery led to the formation of liquid crystalline phases.
Zwitterionic Aza-Claisen Rearrangements Controlled by Pyrrolidine Auxiliaries - Useful Key Steps in Convergent Enantioselective Syntheses
2012
Chiral pyrrolidine substituents served as efficient auxiliaries in diastereoselective zwitterionic ketene aza-Claisen rearrangements. Palladium-catalysed N-allylation starting from optically active proline and prolinol derivatives, as well as from (2S,5S)-2,5-dimethoxymethylpyrrolidine, gave various allylamines bearing trisubstituted olefin moieties. Treatment with complex carboxylic acid fluorides in the presence of trimethylaluminium induced activated ketene addition to the nitrogen and subsequent [3,3] sigmatropic rearrangement to give γ,δ-unsaturated amides with excellent simple diastereoselectivities and up to 11:1 auxiliary-induced diastereomeric ratios. Cleavage of the pyrrolidine am…
ChemInform Abstract: Reactivity and Selectivity of ortho-Metalated Rhodium(II) Complexes in C-H Insertion Reactions of α-Diazo Compounds.
2010
Regioselective intramolecular C−H insertion reactions of α-diazo β-keto esters and α-diazo ketones are mediated by Rh2[OOCR]4-x[PC]x (x = 1, 2; PC = ortho-metalated phosphine; R = CH3, C3F7). In particular, the intramolecular transformation of 1-diazo-5-methyl-3-propyl-2-hexanone catalyzed by Rh2[OOCCH3]2[PC]2 (PC = (C6H4)P(C6H5)2, head-to-tail (H−T) configuration) afforded only the tertiary C−H insertion product. By comparison, no C−H insertion reaction was promoted by doubly metalated complexes with a head-to-head (H−H) configuration. Rh2[OOCR]3[PC] compounds were found to be less suited for these type of reactions.