Preparation of fatty 3,5-disubstituted isoxazole compounds from FA esters

Long-chain fatty compounds containing an isoxazole heterocyclic ring system substituted at the 3- and 5-ring positions were prepared in moderate to good yields (40–64%) in one pot by condensing FA esters such as methyl palmitate, stearate, oleate, or linoleate with the lithiated anion of N-(isopropylidene)isopropylamine followed by dehydrative cyclization. This approach allows readily available FA esters to be utilized and incorporated into the construction of the isoxazole ring system. These novel products were isolated then characterized by NMR, IR spectroscopy, GC-MS, and m.p. Mass spectra of the fatty isoxazole compounds, derived utilizing EI ionization, showed distinctive cleavage patterns that occurred uniformly along the fatty alkyl chain allowing the position of double bonds to be readily located. Two prominent ions at m/z 97 and 110 were common to all the fatty isoxazole compounds examined and were presumably from a McLafferty rearrangement and a cyclization displacement reaction, respectively.