Reduction of fatty ester Δ2-isoxazoline heterocycles. Preparation of fatty esters containing the β-hydroxy ketone moietyheterocycles. Preparation of fatty esters containing the β-hydroxy ketone moiety

Fatty ester compounds containing the β-hydroxy ketone moiety were prepared in good yields from their corresponding fatty Δ²-isoxazoline heterocyclic precursors by a reductive hydrogenolysis-hydrolysis procedure using Raney nickel as catalyst. By this methodology, C-17, C-18, and C-19 straight-chain fatty methyl esters containing the 10-hydroxy 12-keto moieties were prepared in 73, 83, and 92%, respectively, from their corresponding isoxazoline fatty ester compounds. Two other 10-hydroxy 12-keto C-12 and C-14 fatty ester compounds were prepared in 84 and 92% yield, respectively. The C-12 β-hydroxy ketone contains a phenyl ring at C-12, whereas the C-14 β-hydroxy ketone compound has two methyl substituents at C-13. GC-MS using electron impact ionization was used to determine the hydroxyl and ketone positions after conversion of the hydroxyl group into its corresponding trimethylsilyl ether. The precursor fatty ester Δ²-isoxazolines used in this study are readily available in one step from a 1,3-dipolar cycloaddition reaction between nitrile oxides and methyl 10-undecenoate. This overall two-step sequence, 1,3-dipolar cycloaddition followed by reductive ring opening, represent a convenient method to construct fatty ester compounds in good yields containing the β-hydroxy ketone functionality, an outcome not easily accessible by other methods.