The photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction. Part 10: intramolecular reactions involving alk-4-enols and 1,4-dicyanobenzene

1995 ◽  
Vol 73 (12) ◽  
pp. 2158-2169 ◽  
Author(s):  
Kimberly A. McManus ◽  
Donald R. Arnold
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Photoinduced Electron Transfer ◽  
Radical Cations ◽  
Aromatic Substitution ◽  
Radical Ions ◽  
X Ray ◽  
X Ray Crystallography ◽  
Nuclear Magnetic Resonance Spectra ◽  
Intramolecular Reactions ◽  
Acetonitrile Solutions

Our study of the photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction has been extended to include alk-4-enols. Irradiation of acetonitrile solutions of the alk-4-enols, 6-methyl-5-hepten-2-ol (16) and 5-methyl-5-hexen-2-ol (17), and the aromatic, 1,4-dicyanobenzene (1), leads to cyclized 1:1 (alk-4-enol:aromatic) adducts. The addition of biphenyl (5) to the irradiation mixture, serving as a codonor, increases the yields and the efficiency of formation of the adducts. The structures assigned to the products trans-2-(isopropyl 4-cyanophenyl)-5-methyltetrahydrofuran (18, 29%) and cis-2-(isopropyl 4-cyanophenyl)-5-methyltetrahydrofuran (19, 24%) from 16 (reaction [5]), and r-2-(methyl 4-cyanophenyl)-2,t-5-dimethyltetrahydrofuran (20, 13%), r-2-(methyl 4-cyanophenyl)-2,c-5-dimethyltetrahydrofuran (21, 7%), r-3-(4-cyanophenyl)-3,t-6-dimethyltetrahydropyran (22, 11%), and r-3-(4-cyanophenyl)-3,c-6-dimethyltetrahydropyran (23, 2%), from 17 (reaction [6]), rests mainly upon analysis of the 1H and 13C nuclear magnetic resonance spectra. The structures of 19, 22, and 23 were firmly established by X-ray crystallography. The observed ratio of regioisomers indicates a strong preference for 1,5-exo-trig, relative to 1,6-endo-trig, cyclization of the intermediate alk-4-enol radical cation. The mechanistic implication of these results is discussed. Keywords: photoinduced electron transfer, radical ions, cyclization of radical cations, intramolecular reactions of radical cations.

The photochemical nucleophile–olefin combination, aromatic substitution (photo-NOCAS) reaction. Part 11: Involving (R)-(+)-α-terpineol and (R)-(+)-limonene, substituting on 1,4-dicyanobenzene

1996 ◽  
Vol 74 (4) ◽  
pp. 602-612 ◽  
Author(s):  
Donald R. Arnold ◽  
Dennis A. Connor ◽  
Kimberly A. McManus ◽  
Pradip K. Bakshi ◽  
T. Stanley Cameron
Keyword(s):  
Electron Transfer ◽  
Photoinduced Electron Transfer ◽  
Nmr Spectra ◽  
Radical Cations ◽  
Acetonitrile Solution ◽  
Aromatic Substitution ◽  
X Ray ◽  
X Ray Crystallography ◽  
Intramolecular Reactions ◽  
C Nmr

Irradiation of an acetonitrile–methanol (3:1) solution of 1,4-dicyanobenzene (1), biphenyl (5), and (R)-(+)-limonene (21) leads to formation of the 1:1:1 (methanol:21:1) photo-NOCAS adducts: 4-[(1R,2S,4R)-4-isopropenyl-2-methoxy-1-methylcyclohexyl]benzonitrile (23, 30%), 4-[(1S,2R,4R)-4-isopropenyl-2-methoxy-1-methylcyclohexyl]benzonitrile (24, 2%), 4-[(1R,2R,5R)-5-isopropenyl-2-methoxy-2-methylcyclohexyl]benzonitrile (25, 3%), and 4-[(1S,2S,5R)-5-isopropenyl-2-methoxy-2-methylcyclohexyl]benzonitrile (26, 1%). When an acetonitrile solution (no added methanol) of 1,4-dicyanobenzene (1), biphenyl (5), and (R)-(+)-α-terpineol (22) was irradiated under these conditions, the products were the cyclized 1:1 (22:1) photo-NOCAS adducts: (1R,2S,5R)-2-(4-cyanophenyl)-2,6,6-trimethyl-7-oxabicyclo[3.2.1]octane (27,21%) and (1S,4R,6R)-6-(4-cyanophenyl)-1,3,3-trimethyl-2-oxabicyclo[2.2.2]octane (28, 2%). Structural assignments were based primarily upon detailed analysis of 1H and 13C nmr spectra and, for four of the products (24, 26, 27, and 28), structures were firmly established by X-ray crystallography. The mechanism for the formation of these products is discussed, with emphasis on the intramolecular reactions of the intermediate alkene radical cations. Molecular mechanics (MM3) calculations gave information regarding the structure and energy of the conformers of 21 and 22 that was useful for predicting/explaining the observed reactivity on the basis of approach vector analysis; the transition state for cyclization incorporates the nucleophile and the alkene radical cation carbon atoms at the vertices of an obtuse triangle orthogonal to the plane of the π-system. Key words: photoinduced electron transfer, radical cations, cyclization, terpenes.

Structure and nuclear magnetic resonance spectra of 6-bromo-3,3′,4′,5,7-penta-O-methylcatechin

1985 ◽  
Vol 63 (8) ◽  
pp. 2176-2180 ◽  
Author(s):  
F. W. B. Einstein ◽  
E. Kiehlmann ◽  
E. K. Wolowidnyk
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Title Compound ◽  
Bromine Atom ◽  
Heterocyclic Ring ◽  
Equatorial Orientation ◽  
X Ray ◽  
X Ray Crystallography ◽  
Nuclear Magnetic Resonance Spectra ◽  
Ring Conformations

The title compound has been synthesized by selective debromination of 6,8-dibromocatechin and indirect methylation of the resulting 6-bromocatechin via its pentaacetate. The structure of C20H23BrO6 has been determined by X-ray crystallography. The compound crystallizes in the space group P1 with a = 9.589(3) Å, b = 11.576(3) Å, c = 11.326(3) Å, α = 118.80(3)°, β = 93.23(3)°, γ = 111.44(3)°, ρc = 1.481 g cm−3, and Z = 2. Intensities were measured for 2584 independent reflections (2θ < 45°) of which 2213 were observed (I > 3.0σ(I)) and used in subsequent refinement (final R values were R = 0.0268 and Rw = 0.0344). Crystallographic and pmr data confirm the position of the bromine atom at C-6, the trans-diaxial arrangement of H-2/H-3 and the quasi-equatorial orientation of the 3,4-dimethoxyphenyl group (ring B). The two heterocyclic ring conformations are consistent with the expected flexibility of the molecule.

Synthesis, 1H, 13C, and 29Si nuclear magnetic resonance spectra and crystal structure of trans-1,4-diphenyldecamethylcyclohexasilane

1987 ◽  
Vol 65 (2) ◽  
pp. 437-440 ◽  
Author(s):  
Kanta Kumar ◽  
Morton H. Litt ◽  
Raj K. Chadha ◽  
John E. Drake
Keyword(s):  
Crystal Structure ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Coupling Reaction ◽  
Chair Conformation ◽  
Site Symmetry ◽  
X Ray ◽  
X Ray Crystallography ◽  
Nuclear Magnetic Resonance Spectra ◽  
Phenyl Rings

The coupling reaction between PhMeSiCl2 and Me2SiCl2 in the presence of Na/K alloy resulted in a variety of phenylated permethylcyclohexasilanes of which only trans-1,4-Ph2Me10Si6 could be obtained in pure form by repeated recrystallizations. It was studied by means of nmr (1H, 13C, and 29Si) and X-ray crystallography. The crystals are monoclinic, P21/c with a = 10.105(6), b = 14.77(1), c = 9.973(6) Å, β = 94.08(5)°, V = 1485(2) Å3, and Z = 2 for 1922 unique "observed" reflections and the structure refined to an R index of 0.036. The molecule has site symmetry [Formula: see text] and the chair conformation of cyclohexane, with the two phenyl rings occupying the equatorial positions.

Conformational analysis of functionalized sultines by nuclear magnetic resonance and x-ray crystallography. Application of a generalized Karplus equation

1983 ◽  
Vol 105 (16) ◽  
pp. 5406-5414 ◽  
Author(s):  
C. A. G. Haasnoot ◽  
R. M. J. Liskamp ◽  
P. A. W. Van Dael ◽  
J. H. Noordik ◽  
H. C. J. Ottenheijm
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Conformational Analysis ◽  
Karplus Equation ◽  
X Ray ◽  
X Ray Crystallography ◽  
Nuclear Magnetic

The crystal structure of ethyl-Z-3-amino-2-benzoyl-2-butenoate and measurement of the barrier to E,Z-isomerization

1980 ◽  
Vol 58 (17) ◽  
pp. 1821-1828 ◽  
Author(s):  
Gary D. Fallon ◽  
Bryan M. Gatehouse ◽  
Allan Pring ◽  
Ian D. Rae ◽  
Josephine A. Weigold
Keyword(s):  
Crystal Structure ◽  
Nuclear Magnetic Resonance ◽  
Hydrogen Bond ◽  
Free Energy ◽  
Magnetic Resonance ◽  
Energy Of Activation ◽  
X Ray ◽  
X Ray Crystallography ◽  
Free Energy Of Activation ◽  
Nuclear Magnetic

Ethyl-3-amino-2-benzoyl-2-butenoate crystallizes from pentane as either the E (mp 82–84 °C) or the Z-isomer (mp 95.5–96.5 °C). The E isomer is less stable, and changes spontaneously into the Z, which bas been identified by X-ray crystallography. The structure is characterised by an N–H/ester CO hydrogen bond and a very long C2—C3 bond (1.39 Å). Nuclear magnetic resonance methods have been used to measure the rate of [Formula: see text] isomerization at several temperatures, leading to the estimate that the free energy of activation at 268 K is 56 ± 8 kJ.

Synthesis and conformation studies by x-ray crystallography and nuclear magnetic resonance of cyclo(L-Phe-L-Pro-D-Ala)2

1984 ◽  
Vol 106 (13) ◽  
pp. 3844-3850 ◽  
Author(s):  
Gopinath Kartha ◽  
K. Krishna Bhandary ◽  
Kenneth D. Kopple ◽  
Anita Go ◽  
Peng Peng Zhu
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
X Ray ◽  
X Ray Crystallography ◽  
Nuclear Magnetic

scholarly journals Supersize Cp! Tetrabenzo[a,c,g,i]fluorenyl complexes of yttrium

2017 ◽  
Vol 95 (4) ◽  
pp. 363-370 ◽  
Author(s):  
Jianlong Sun ◽  
David J. Berg ◽  
Brendan Twamley
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Ethylene Polymerization ◽  
Nmr Studies ◽  
X Ray ◽  
X Ray Crystallography ◽  
Trinuclear Cluster ◽  
Polymerization Catalyst ◽  
Dynamic Nuclear Magnetic Resonance ◽  
Trimethylsilyl Isocyanate

The synthesis of tetrabenzo[a,c,g,i]fluorenyl (Tbf) yttrium dialkyl complexes, (Tbf)Y(CH2SiMe3)2(L) (L = tetrahydrofuran (THF), 1; L = bipy, 2), by direct protonolysis of the tris(alkyl) complex, Y(CH2SiMe3)3(THF)2, are reported. The X-ray crystal structures of 1 and 2 display the helical twisting typically observed for the Tbf ligand. Dynamic nuclear magnetic resonance (NMR) studies on 1 show a barrier to Tbf helical inversion (epimerization or “wagging”) of 38.1 ± 0.5 kJ mol−1. The reaction of 1 with acidic hydrocarbons such as 1,3-bis(trimethylsilyl)cyclopentadiene or trimethylsilylacetylene results in protonolysis to form the mixed Cp derivative [(Tbf){C5H3(SiMe3)2}Y(CH2SiMe3)(THF)] (3) or [(Tbf)Y(CCSiMe3)2(THF)]n (4), respectively. In the case of 4, a small amount of the trinuclear cluster (Tbf)Y3(μ3-CCSiMe3)2(μ2-CCSiMe3)3(CCSiMe3)3(THF)2 (5) was isolated and characterized by X-ray crystallography. Dialkyl 1 undergoes smooth insertion of trimethylsilyl isocyanate to afford [(Tbf)Y{κ2-(N,O)-Me3SiN(Me3SiCH2)CO}2(THF)] (6) but it does not react with alkenes. Treating 1 with [Ph3C]+[B(C6F5)4]− in bromobenzene generates a moderately active ethylene polymerization catalyst (36 kg mol−1 h−1 bar−1).

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