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

Abstract

AbstractFatty 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.