π-Facial stereoselectivity in the Diels–Alder reactions of benzene oxides

1991 ◽  
Vol 69 (9) ◽  
pp. 1337-1343 ◽  
Author(s):  
James R. Gillard ◽  
Michael J. Newlands ◽  
John N. Bridson ◽  
D. Jean Burnell
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Steric Hindrance ◽  
Diels Alder ◽  
Dimethyl Acetylenedicarboxylate ◽  
X Ray ◽  
Orbital Interactions ◽  
Nuclear Magnetic Resonance Spectra ◽  
Nuclear Overhauser ◽  
Benzene Oxide

The Diels–Alder reactions of N-phenylmaleimide and dimethyl acetylenedicarboxylate with benzene oxide (1,3,5-cyclohexatriene 1,2-oxide, 3) and its more substituted derivatives 1,2-dimethyl-1,3,5-cyclohexatriene 1,2-oxide (7) and 10-oxatricyclo[4.3.1.0]deca-2,4-diene (11) in a kinetic manner gave exclusively products of addition anti to the plane-nonsymmetrical oxygen. The structures of the adducts were determined unequivocally by nuclear Overhauser enhancements in their 1H nuclear magnetic resonance spectra and by X-ray crystallographic methods. The π-facial stereoselectivity was rationalized in terms of unfavorable orbital interactions, steric hindrance between the dienophile and the syn face of benzene oxide, and σ-donation by the oxygen. Key words: cycloaddition, Diels–Alder, syn-anti, π-facial stereoselectivity, benzene oxide.

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.

13C N.M.R. STUDIES: VIII. 13C SPECTRA OF SOME SUBSTITUTED ANISOLES

1966 ◽  
Vol 44 (23) ◽  
pp. 2855-2866 ◽  
Author(s):  
K. S. Dhami ◽  
J. B. Stothers
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Aromatic Ring ◽  
Steric Hindrance ◽  
Steric Effect ◽  
Chemical Shifts ◽  
Methoxyl Group ◽  
Side Chains ◽  
Nuclear Magnetic Resonance Spectra ◽  
Magnetic Resonance Spectra

The 13C nuclear magnetic resonance spectra of a series of 40 substituted anisoles have been obtained to investigate the effects of substitution on the aromatic and methoxyl carbon shieldings. This work extends our studies on the variations of chemical shifts of carbon nuclei in side chains of aryl derivatives. The question of steric hindrance to conjugative interaction of a methoxyl group with an aromatic ring is considered on the basis of the present results. Evidence of a steric effect in compounds in which both ortho positions are substituted is presented.

The Synthesis of Organometallic YlidesInteraction of Methylenetriphenylphosphorane with Bis(η5-cyclopentadienyl)-zirconium and -hafnium Dichlorides and the Molecular Structure of Bis(η5 -Cyclopentadienyl)chlorozirconylmethylenetriphenylphosphorane

1980 ◽  
Vol 35 (10) ◽  
pp. 1289-1297 ◽  
Author(s):  
James C. Baldwin ◽  
N. L. Keder ◽  
Charles E. Strouse ◽  
William C. Kaska
Keyword(s):  
Molecular Structure ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Bond Length ◽  
Zirconium Complex ◽  
Kcal Mole ◽  
Hindered Rotation ◽  
X Ray ◽  
Nuclear Magnetic Resonance Spectra ◽  
Yellow Orange

Abstract The interaction of (η5-C5H5)2MCl2 (M = Zr, Hf) with excess C̅H2-P⁺Ph3 in THF gives (η5-C5H5)2MCl(C̅H-P⁺Ph3) as yellow orange needles. Nuclear magnetic resonance spectra show hindered rotation about the P⁺-C̅ bond with ⊿G≠= 8.6 kcal/mole for M = Zr and 8.3 kcal/mole for M - Hf, respectively. The X-ray molecular structure of the zirconium complex shows a relatively short Zr-C bond length of 2.152 Å and a long P⁺-C̅ bond length of 1.716 Å.

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