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SPECTROPHOTOMETRIC STUDY OF DIENESTROL PHOTOISOMERIZATION
Author(s) -
Doyle T. D.,
Benson W. R.,
Filipescu N.
Publication year - 1978
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1978.tb07556.x
Subject(s) - chemistry , photoisomerization , tautomer , isomerization , moiety , photochemistry , sigmatropic reaction , phenanthrene , steric effects , stereochemistry , organic chemistry , catalysis
Abstract— Photolysis of synthetic estrogen dienestrol resulted in formation of a 4a,4b‐dihydrophenanthrene, a rare example of a stable intermediate of the classical stilbene → phenanthrene photocyclization. Time‐lapse spectrometric investigation suggested an initial cis‐trans isomerization in the dimethylbuta‐dime moiety of dienestrol followed by a photochemical [1, 51 sigmatropic proton transfer which converted the two cross‐conjugated p ‐hydroxystyrene halves into a vinyl‐stilbene. A subsequent electrocyclic ring‐closure in an electronically excited state generated a cyclic nonaromatic heptenediol. This last photoproduct tautomerized rapidly in the dark to a stable, crystalline, tricyclic pentenedione. The final diketone product is an example of a 4a.4b‐dihydrophenanthrene self‐stabilized by a double ketoenol tautomerism. The three sequential photoisomerizations of dienestrol are made possible by a fortuitous coincidence of steric and orbital symmetry requirements.