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Photochemical reactions, 135th communication Photochemistry of Homoconjugated Cyclobutanones. II. Decisive Effect of gem ‐ Dimethyl Substitution on the Course of the Oxa‐di‐π‐methane Rearrangement
Author(s) -
Lyle Terry A.,
Mereyala Hari Babu,
Pascual Alfons,
Frei Bruno
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.19840670319
Subject(s) - chemistry , isomerization , double bond , moiety , photochemistry , photodissociation , ring (chemistry) , cope rearrangement , medicinal chemistry , stereochemistry , catalysis , organic chemistry
The synthesis and photolysis of the spirocyclobutanones 4–7 incorporating a cyclohexa‐, cyclohepta‐ and cyclooctadiene moiety, respectively, is described. On triplet excitation, these compounds undergo isomerization via a 1,2‐acyl shift involving one or both double bonds of the diene system. The presence of a gem ‐dimethyl group as in 1 , 4 and 7 dramatically changes the photoproduct distribution, since only these substrates leads to the products 3, 29 and 34 resulting from vinylogous ring closure ( Scheme 5 ). Those substrates without methyl substitution ( 5 and 6 ) give only products of a rearrangement involving one double bond.