Hydroboration of Fats. I. Positional Isomerism in the Methyl Oleate Hydroboration Reaction

Abstract

It has been found that addition of diborme to the ethylenic bond of methyl oleate proceeds smoothly without significant reduction of the carbomethoxy group. Alkaline hydrogen peroxide oxidation of the tris(carbomethoxyalky1)borane resulted in the formation of an equimolar mixture of 9-and 10-hydroxyoctadecanoic acids, establishing that the hydroboration reaction proceeded nonselectively. Little or no isomerization occurred on heat treatment of these substituted trialkyl boranes.

Hydroboration of unsaturated fatty acid methyl esters and conversion of the boron adducts*

“…The structures of 18 and 19 are in accord with their IR, 1 H NMR,13 C NMR, mass spectra, and their elemental analyses. The compounds 18 and 19 show a keto-as well as an ester-carbonyl group in the IR-spectrum.…”

“…With methyl oleate (3a) we found in 90% yield a 1:1mixture of methyl 9-hydroxyoctadecanoate (4a) and methyl 10-hydroxyoctadecanoate (5a) [12] (Scheme 1b). Applying the same conditions but a different work-up Fore and Bickford found in 85% yield a 1:1mixture of 9hydroxyoctadecanoic acid (4b) and 10-hydroxyoctadecanoic acid (5b) [13] (Scheme 1b). We avoided the use of thexylborane, disiamylborane, and 9-borabicyclo[3.3.1]nonane for the hydroboration-oxidation of the esters 3a, 6a, and 9a, because the yields were poor with these reagents.…”

“…THF (30 mL) with the BH 3 · THF complex (1.85 mL, 1.8 m, 3.33 mmol BH 3 ). The preparation of the BH 3 · THF complex and the determination of the borane content are described in [10][11][12][13]. In all cases, we used a self-prepared BH 3 · THF complex.…”

“…After cooling to RT, water (1 mL) is added and then a 3 N NaOH-solution (1.5 mL) and a 30% H 2 O 2 -solution (1.5 mL) are added. The solution is stirred for 1 h at RT and then diluted with water (10 mL); for salting out NaCl-salt is added and thereafter the solution is extracted with diethyl ether (3 Â 10 mL) and dried (MgSO 4 13 (16) 18-Hydroxystearic acid (1 g, 3.33 mmol) [14] dissolved in abs. THF (10 mL) is added dropwise to a suspension of LiAlH 4 (190 mg, 5.00 mmol) in abs.…”

Hydroboration of Methyl Esters of Fatty Acids

“…However, it has been demonstrated that reducing the ester groups is much slower than that of olefins (Brown & Keblys, 1964). By using suitable operating conditions, it is possible to limit this secondary reaction and to obtain a selective reaction of carboncarbon double bond (Fore & Bickford, 1959). Others have protecting ester function by a silyl group in order to have a single reactive site (Kabalka & Bierer, 1989).…”