Journal of the Chemical Society. Perkin transactions I p. 1383 - 1388 (1987)
Update date:2022-08-23
Topics:
Bonnett, Raymond
Hamzetash, Dariush
Valles, Maria Asuncion
The Z <*> E photoisomerisation of four α-unsubstituted pyrromethenones which are potential precursors of alkanol-propentdyopent adducts is studied using a direct n.m.r. spectroscopic approach in CD3OD-CDCl3.Chemical-shift assignments are made with the help of n.O.e. and decoupling experiments.For the polyalkylpyrromethenones the photostationary state contains ca. 25percent of the E isomer: a system with a β-ethoxycarbonyl group leads to 43percent E isomer at photoequilibrium.The E isomers can be manipulated in solution without appreciable change, but thermodynamic equilibration to the Z isomer (ca. 99percent) occurs on dry silica.A similar photoisomerisation of (4Z,15Z)-bilirubin IIIα in ND3-CD3OD leads to a photoequilibrated mixture containing 16percent of (4E,15Z)-bilirubin IIIα.
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