71007-11-9Relevant academic research and scientific papers
Deuterium isotope effects on 13C chemical shifts of enaminones
Zheglova, Donka Kh.,Genov, Daniel G.,Bolvig, Simon,Hansen, Poul Erik
, p. 1016 - 1023 (2007/10/03)
Deuterium isotope effects on 13C chemical shifts have been studied in a series of substituted N-alkyl and N-phenyl keto-enamines. The intramolecularly hydrogen bonded Z-forms show the largest two-bond isotope effects, 2δC-1 (ND). Methyl-substitution at C-1 leads to a larger two-bond isotope effect in the N-phenyl-substituted derivatives. This effect is ascribed to steric compression. Space-filling substituents at the ortho-position of the N-phenyl ring lead to a decrease of the two-bond isotope effect. A correlation is found between 2δC-1(ND) and 3δC-2′(ND). The latter becomes negative in the sterically hindered cases. 3δC-2′(ND) may therefore be used as a gauge of the twist of the phenyl ring. o-Hydroxy substitution of the CO-phenyl rings enables intramolecular hydrogen bonding to the carbonyl group. This kind of hydrogen bond with two donors to one acceptor leads to smaller 2δC-2(ND) and 2δC-2″(OD) isotope effects equivalent to weaker hydrogen bonds for the Z-isomer. This is ascribed to competition for the acceptor. For the E-isomer 2δC(OD) is enhanced. The same feature is seen for N,N-dimethylamino enamines. This increase is ascribed to delocalization of the nitrogen lone-pair onto the carbonyl oxygen, thereby strengthening the hydrogen bond and thus leading to larger two-bond, 2δC(OD), isotope effects. Acta Chemica Scandinavica 1997.
Vinylogous Acyl Compounds. XIX. Vinylogous Acyl Group Migration in 2-Aminophenol. A Contribution to the Isomerization Mechanism of Mixed Diacyl Derivatives of 2-Aminophenol
Fischer, Gerhard W.
, p. 99 - 124 (2007/10/02)
Starting with 2-acylaminophenols 5 and 2-(2-acylvinylamino)-phenols 6 the N-acyl O-acylvinyl derivatives 7 of 2-aminophenol and their N-acylvinyl O-acyl isomers 8 were prepared and characterized.These vinylogous acyl compounds are able to isomerize in the same manner as simple O,N-diacylated 2-aminophenols 3 and 4, which under suitable conditions easily rearrange to give a dynamic equilibrium 34.Contrary to 3 and 4, however, the isomerization of 7 and 8 can be followed directly by spectroscopic methods, so that vinylogs of this type are useful model systems forstudying acyl group migrations in 2-aminophenol.Kinetic measurements show that the mutual rearrangement of 7 and 8 is a reversible general based catalyzed reaction, being first order with respect to substrate and catalyst.The isomerization of the N-acetyl derivatives 7a-h as well as the N-benzoyl derivatives 7i-p results in strictly linear HAMMETT correlations with positive reaction constant ρ.In the case of 7a-h the equilibrium constant K and the forward and reverse velocity constants k1 and k2 (including activation parameters) could be determined.The kinetic investigations and additional non-kinetic experiments indicate that the catalyst acts as proton acceptor and not - as hitherto supposed - as acyl group transferring nucleophile.Based on the findings an isomerization mechanism for mixed diacyl derivatives of 2-aminophenol is suggested.
