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Anionic and Photochemical Behaviour of the Medium‐Sized Terpenoid Ketone 8‐Dehydro‐12‐ O ‐methyl‐deacylhallerin
Author(s) -
Croce Gianluca,
Milanesio Marco,
Viterbo Davide,
Clericuzio Marco,
Ugliengo Piero,
Appendino Giovanni
Publication year - 2006
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200600107
Subject(s) - chemistry , isomerization , epimer , ketone , conformational isomerism , keto–enol tautomerism , double bond , molecular dynamics , nuclear magnetic resonance spectroscopy , computational chemistry , molecular mechanics , stereochemistry , photochemistry , organic chemistry , molecule , tautomer , catalysis
Treatment of the germacrane ketone 8‐dehydro‐12‐ O ‐methyl‐deacylhallerin ( 2 ) with bases under conditions of thermodynamic enolization resulted in complete epimerization at the adjacent carbon atom C‐7, with formation of 3 . The conformational features of the epimeric ketones 2 and 3 were investigated by X‐ray crystal structure analysis, NMR spectroscopy, molecular mechanics and dynamics simulations and ab initio calculations. While 2 showed temperature‐insensitive sharp 1 H NMR signals, its epimer 3 showed only broad lines. These spectral features suggest that 2 is monorotameric, while 3 is a mixture of different conformers, as was verified by molecular mechanics and dynamics calculations. Upon UV irradiation, 2 underwent isomerization at the C1–C10 double bond, while 3 was unreactive. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)