Search results for "Intramolecular force"
showing 10 items of 599 documents
Understanding the domino reactions of alkyne-tethered N-tosylhydrazones yielding fused polycyclic pyrazoles. An MEDT study
2019
Abstract The domino reactions of alkyne-tethered N-mesylhydrazones yielding fused polycyclic pyrazoles have been studied within the Molecular Electron Density Theory (MEDT). Analysis of the Gibbs free energies indicates that the more favourable reactive path is the one in which the elimination of mesylate anion takes place before the intramolecular [3 + 2] cycloaddition (IM32CA) reaction, which corresponds with the rate-determining step of these domino processes. ELF topological analysis of the bond formation along the IM32CA reaction indicates that in spite of the high activation energy associated to this intramolecular reaction, it shows a pmr-type mechanism characterised by the presence …
Stereoselective synthesis of polyoxygenated atisane-type diterpenoids
2001
Abstract A new stereoselective approach to polyoxygenated atisane-type diterpenes starting from (S)-(+)-carvone is described. The key steps involve an intramolecular Diels–Alder reaction, an unusual intramolecular diazo ketone cyclopropanation of an unsaturated ketone, and a regioselective endocyclic cleavage of a cyclopropyl carbinyl radical as key synthetic steps. The synthesis of the bioactive polyoxygenated atisanes atis-16(17)-en-3,14-dione ( 2 ) and 3R-hydroxy-atis-16(17)-en-2,14-dione ( 3 ) following this approach is presented.
Part II. Chiral dirhodium (II) catalysts with ortho-metalated arylphosphane ligands in the enantioselective intramolecular cyclopropanation of a race…
2006
Abstract In this report, chiral dirhodium (II) with ortho -metalated phosphane ligands, namely ( M )-Rh 2 (O 2 CR) 2 (PC) 2 [PC = ortho -metalated aryl phosphane, O 2 CR = carboxylate bridging ligands) ( 1a–g ), have been used for the intramolecular cyclopropanation of racemic1-diazo-6-methyl-3-(2-propenyl)-5-hepten-2-one ( 2 ), containing both a tri- and monosubstituted carbon–carbon double bond, in pentane. The highest level of regiocontrol has been obtained with chiral catalyst Rh 2 (O 2 CCH 3 ) 2 [( p -MeC 6 H 3 )P( p -MeC 6 H 4 ) 2 ] 2 ( M )- 1c , affording favorably trisubstituted cyclopropane 3 versus monosubstituted cyclopropane 4 in 74:26 ratio. An exceptional diastereoselectivity…
Photochemical Transformations of Some Neoclerodane and Labdane Diterpene Ketones
1999
Some neoclerodane (2–4) and labdane (5 and 6) diterpene ketones having a β- or γ-hydroxy function, an α-epoxy group, or an α-olefinic double bond have been irradiated at λ = 313 nm in dry solvents (benzene or methanol). Fruticolone (2) yielded the naturally occurring 5,6-seco-neoclerodan-6,1α-olide derivative fruticolide (1), while hispanolone (5) gave the δ-lactone 8, both transformations involving a Norrish type I photoreaction. The α,β-unsaturated ketone derivative 4 was transformed into 7 by a stereoselective intramolecular [2+2] cycloaddition reaction involving its furanic 13(16)-double bond. Finally, the α-epoxy ketone 6 was rearranged to the 10(98)abeo-labda-7,9-dione derivative 10. …
Highly Diastereoselective Arylation of (S)-Mandelic Acid Enolate: Enantioselective Synthesis of Substituted (R)-3-Hydroxy-3-phenyloxindoles and (R)-B…
2005
An easy access to substituted (R)-3-hydroxy-3-phenyloxindoles, (R)-benzylic acids, and benzophenones is described. The reaction of the lithium enolate of the (2S,5S)-cis-1,3-dioxolan-4-one derived from optically active (S)-mandelic acid and pivalaldehyde with several o- and p-halonitrobenzenes proceeds readily to give the corresponding arylation products in good yields and diastereoselectivities. The reduction of the nitro group with Zn/HCl/EtOH in the o-nitro arylation products with concomitant intramolecular aminolysis of the dioxolanone moiety leads directly to enantiomerically pure (R)-3-hydroxy-3-phenyloxindoles. On the other hand the basic hydrolysis of the dioxolanone moiety in all t…
Synthesis of β-d-mannosides from β-d-glucosides via an intramolecular Sn2 reaction at C-2
1992
Abstract The selective synthesis of β- d -mannosides was achieved by first synthesizing β- d -glucosides that carry a N -phenylcarbamoyl protecting group at O-3. These derivatives were transformed into the corresponding β- d -mannosides by intramolecular nucleophilic substitution with inversion of configuration at C-2, the O -triflyl group being the leaving group. Subsequent intramolecular attack of the neighboring carbamoyl group resulted in the formation of the 2,3-carbonate of the desired β d -mannoside.
Photoconductivity of Poly(Arylenevinylene)S and Poly(Hetarylenevinylene)S
1994
Abstract The intramolecular condensation of aromatic Schiff bases leads under strong alkaline conditions to the poly(arylenevinylene)s and poly(hetarylenevi-nylene)s A - H. Due to the extreme stereoselectivity the resulting products are rigid, (E)-configurated polymers. The broad band gap of the unsubstituted intrinsic insulators is decreased by alkoxy substituents. Investigations of the photoconductivity and the photoreactivity, as well as of the AC-conductivity of some undoped, doped and quaternized systems are performed.
The role of intermolecular forces in contact electrification on polymer surfaces and triboelectric nanogenerators
2019
This research was supported by the European Regional Development Fund within the project ‘‘Hybrid energy harvesting systems’’ 1.1.1.1./16/A/013.
Assembling Magnetic Blocks: A Strategy to Control the Nuclearity and Magnetic Properties of Polynuclear Complexes
1996
Synthetic strategies dealing with the polymerization of either di-μ-hydroxocopper(II) complexes or 2,2′-bipyrimidine (bpym)-containing first row transition metal ions allow the preparation of polynuclear compounds whose structures and magnetic properties are presented here. The influence of structural and chemical parameters on the magnitude of the singlet-triplet energy gap (J) in di-μ-hydroxocopper(II) complexes [LCu(OH)2CuL]2+ with L = 2,2′-bipyridine (bpy) and bpym is analyzed and discussed. Special attention is devoted to nature of the counterion which allows the preparation of hydroxo-bridge copper(II) cubane and double cubane type complexes where all the intramolecular magnetic inter…
Tandem asymmetric Michael reaction-intramolecular Michael addition. An easy entry to chiral fluorinated 1,4-dihydropyridines.
2010
A novel one-pot tandem asymmetric Hantzsch-type process has been employed to generate fluorinated 1,4-dihydropyridines (1,4-DHPs) as single diastereoisomers. It involves the condensation of (R)-(+)-allyl p-tolyl sulfoxide, fluorinated nitriles, and alkyl propiolates, giving access to a new family of enantiomerically pure fluorine-containing 1,4-DHPs.