ヨウ素を増感剤とした1, 4-ジエン化合物の光共役化反応

概要

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In the course of studies on the iodine-sensitized photoconjugation of 1, 4-diene compounds, the effects of terminal functional groups on this reaction were investigated. Linoleic acid and its related compounds, such as methyl linoleate, linoleyl alcohol, linoleyl acetate and cis-6, cis-9-octadecadiene derived from linoleic acid, were used as samples.<BR>Based on the results of sensitized isomerization, the carboxyl group was without any effect whatsoever. Linoleic acid reacted at the same rate as 6, 9-octadecadiene, or faster than that of methyl linoleate, so that maximum equilibrium was attained within 1h. Moreover, the photo-conjugation of linoleyl acetate occurred more slowly than that of methyl linoleate. The amounts of the conjugated compounds were about as much as 80% in either case. With linoleyl alcohol, isomerization was quite slow, the yield being about 10% after 8h. This is in agreement with the finding that this sensitized conjugation does not proceed in a polar solvent such as ethanol.<BR>Therefore, the reactivities of the end-groups on this iodine-sensitized reaction decrease in the following order : CH3≥COOH>COOCH3>CH2OCOCH3>>CH2OH.<BR>This reaction apparently occurs through a radical mechanism involving a bridged iodoalkyl radical as an intermediate. The products mainly consisting of cis, trans- and trans, trans-conjugated dienes were thus obtained at a ratio of about 3 : 7.