Journal of the Chemical Society. Perkin transactions II p. 1479 - 1486 (1984)
Update date:2022-08-30
Topics:
Benassi, Rois
Folli, Ugo
Iarossi, Dario
Schenetti, Luisa
Taddei, Ferdinando
A conformational study of formyl and acetyl derivatives of benzofuran provides evidence that in the case of 2- and 7-derivatives the E,Z-conformational mixture is solvent dependent, the Z-form prevailing in solvents with higher polarity.The presence of the same substituents in the 3- and 4-position gives compounds with predominantly Z-conformation and no change is caused by solvents.These results show an interestingly different behaviour by carbonyl derivatives of benzofuran with respect to the same benzothiophene derivatives.The conformational analysis was carried out by the n.m.r. method by employing (1)H and (13)C chemical shifts, long-range proton-proton coupling constants, and lanthanide-induced shifts (LIS) simulation.For the derivatives substituted in position 7, the LIS method is not a suitable approach for the determination of the conformer populations since, in solution, a chelate is formed where bonding of Eu to the oxygen atoms of the carbonyl and of the heterocyclic ring stabilizes the Z-form.A quantitative approach for determining the relative conformer populations of benzofuran-7-carbaldehyde was set up by statistical manipulation of long-range proton-proton coupling constants, proton chemical shifts, and the classical of dielectrics.
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