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Zur Photochemie des Caryophyllens und des iso ‐Caryophyllens Umlagerungen ihrer 1,5‐Diensysteme nach direkter π,π*‐Anregung in flüssiger Phase
Author(s) -
SchulteElte K. H.,
Ohloff G.
Publication year - 1971
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19710540142
Subject(s) - chemistry , photoisomerization , isomerization , double bond , cyclopropane , allylic rearrangement , photochemistry , allene , stereospecificity , cyclopropene , singlet state , stereochemistry , excited state , medicinal chemistry , ring (chemistry) , organic chemistry , physics , nuclear physics , catalysis
Abstract When caryophyllene ( 1 ) and isocaryophyllene ( 2 ) are irradiated at their π,π*‐ transitions (λ ≤ 253.7 nm) they rearrange relatively rapidly and in high yield to mixtures of isomeric sesquiterpene hydrocarbons. Compounds 3–11 , the structural determinations of which are described, represent 90% of the photoisomers. All the rearrangements involve the 1, 5‐diene systems, and, with the exception of cis ‐ trans isomerizations, fragmentation of the doubly allylic σ‐bond and disappearance of the trisubstituted double bond always occur. The cyclopropane, acetylene, allene, and 1, 5‐diene compounds resulting are the first examples of this type of photo‐isomerization products obtained from unconjugated monomeric 1, 5‐dienes by direct excitation with light. Their formation appears to be stereospecific, and is dependent on the stereochemistry of the double bond system in 1 and 2 . In addition to the cis ‐isomer 2 caryophyllene yields only compounds 3, 4 , and 5 , while from isocaryophyllene, compounds 8, 9, 10 and 11 are formed in addition to 1 . The only isomerization products common to both caryophyllenes ( 1 and 2 ) are 6 and 7 . This behaviour and the lack of positive identification of a biradical (triplet) intermediate lead to the probable conclusion that the greater part of the photoisomerization occurs directly from the excited singlet states. Possible mechanisms for the formation of the photoisomerization products are discussed.