Reaction of mono-epoxidized conjugated linoleic acid ester with boron trifluoride etherate complex

The reaction of methyl 11, 12‐E‐epoxy‐9Z‐octadecenoate (1) with boron trifluoride etherate furnished a mixture of methyl 12‐oxo‐10E‐octadecenoate (3a) and methyl 11‐oxo‐9E‐octadecenoate (3b) in 66% yield. Methyl 9, 10‐Z‐epoxy‐11 E‐octadecenoate (2) with boron trifluoride etherate furnished a mixture of methyl 9‐oxo‐10 E‐octadecenoate (4a, 45%) and methyl 10‐oxo‐11 E‐octadecenoate (4b, 19%). A plausible mechanism is proposed for these reactions, which involves the attack on the epoxy ring system by BF3, followed by deprotonation, oxo formation, and double bond migration to give a mixture of two positional α,β‐unsaturated C18 enone ester derivatives (3a/3b, 4a/4b). The structures of these C18 enone ester derivatives (3a/3b, 4a/4b) were identified by a combination of NMR spectroscopic and mass spectrometric analyses.