Abstract
Oxidative ring opening reaction of methyl 9,12-epoxy-9,11-octadecadienoate ( 1) with excess magnesium monoperoxyphthalate (MMPP) under ultrasonic irradiation in water furnished methyl 9,12-dioxo- cis-10-octadecenoate ( 2, 93%). Reaction of compound 1 with 10 molar equivalents of m-chloroperoxybenzoic acid ( m-CPBA) in dichloromethane gave methyl cis-10,11-epoxy-9,12-dioxooctadecanoate ( 3, 91.5%) exclusively. Under ultrasonic irradiation, compound 1 reacted with m-CPBA to give a mixture of compounds 2 (60%) and 3 (40%). Isomerization of methyl 9,12-dioxo- cis-10-octadecenoate ( 2) to the corresponding trans-isomer (methyl 9,12-dioxo- trans-10-octadecenoate, 4, 95%) was achieved in the presence of pyridine in water under ultrasonic irradiation. Compound 4, alternatively prepared in 95% yield from compound 1 by reaction with pyridinium chlorochromate, was readily epoxidized with hydrogen peroxide to methyl trans-10,11-epoxy-9,12-dioxooctadecanoate ( 5, 95%). The corresponding cis-isomer (methyl 9,12-dioxo- cis-10-octadecenoate, 2) resisted all attempts by MMPP and hydrogen peroxide to be epoxidized. The structures of the various derivatives ( 2– 5) of compound 1 were identified by a combination of spectroscopic techniques including IR, 1H- and 13C-NMR spectroscopy.
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