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Photochemical reactions. 137 th communication . Preparation and photolysis of ( E / Z )‐7‐methyl‐β‐ionone
Author(s) -
Ishii Keitaro,
Mathies Peter,
Nishio Takehiko,
Wolf Hans Richard,
Frei Bruno,
Jeger Oskar
Publication year - 1984
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.19840670502
Subject(s) - chemistry , ionone , isomerization , yield (engineering) , photochemistry , pentane , photodissociation , bromide , chromophore , cyclohexene , medicinal chemistry , stereochemistry , organic chemistry , catalysis , materials science , metallurgy
The title compounds ( E/Z )‐ 7 were prepared in 66% overall yield by reaction of β‐ionone (( E )‐( 1 ) with lithium dimethylcuprate, trapping of the intermediate enolate with benzeneselenenyl bromide and oxidation with H 2 O 2 . Analogously, ( E/Z )‐7‐methyl‐α‐inone (( E/Z )‐ 12 ) was obtained in 65% yield from α‐ionone (( E )‐ 11 ). 1 n, π * ‐ Excitation (λ > 347 nm, pentane) of ( E )‐7 causes rapid ( E/Z )‐isomerization and subsequent reaction of ( Z )‐ 7 to 15 (66%). The formation of 15 is explained by twisting of the dienone chromophore due to repulsive interaction of the 7‐CH 3 ‐group with the CH 3 ‐groups of the cyclohexene ring. On the other hand, irradiation λ > 347 nm, Et 2 O) of ( E )‐ 7 in the presence of acid leads to ( Z )‐ 7 (5%) and to the novel compound 16 (88%).