Ultrasound in fatty acid chemistry: synthesis of a 1-pyrroline fatty acid ester isomer from methyl ricinoleate.
A novel 1-pyrroline fatty acid ester isomer (viz. 8-5-hexyl-1-pyrrolin-2-yl) octanoate) has been synthesized from methyl ricinoleate by two routes with an overall yield of 42 and 30%, respectively. Most of the reactions are carried out under concomitant ultrasonic irradiation (20 KHz, ca. 53 watts/cm2). Under such a reaction condition, the reaction time is considerably shortened, and product yields are high. Dehydrobromination under concomitant ultrasonic irradiation of methyl 9, 10-dibromo-12-hydroxyoctadecanoate with KOH in EtOH furnishes methyl 12-hydroxy-9-octadecynoate (66%) within 15 min. Hydration of the latter under ultrasound with mercury(II)acetate in aqueous tetrahydrofuran yields exclusively methyl 12-hydroxy-9-oxo-octadecanoate (95%) in 30 min. The hydroxy group in the latter compound is transformed to the azido function via the mesylate, and treatment of the azido-oxo intermediate (methyl 12-azido-9-oxooctadecanoate) with Ph3P under ultrasonic irradiation furnishes the requisite 1-pyrroline fatty acid ester (77%). The same azido-oxo intermediate has also been obtained by the oxidation of methyl 12-azido-9-cis-octadecenoate using benzoquinone and a catalytic amount of Pd(II)chloride in aqueous tetrahydrofuran under concomitant ultrasonic irradiation (90 min) to give the product in 45% yield. The latter reaction does not take place even under prolonged silent stirring of the reaction mixture.
Lie Ken Jie
M S
MS
Department of Chemistry, University of Hong Kong.
Syed-Rahmatullah
M S
MS
Lam
C K
CK
Kalluri
P
P
D004952:Esters / Q000138:chemical synthesis*; D005227:Fatty Acids / Q000737:chemistry*; D007536:Isomerism; D011758:Pyrroles / Q000138:chemical synthesis*; D012277:Ricinoleic Acids / Q000737:chemistry*; D014465:Ultrasonics
D004952:Esters; D005227:Fatty Acids; D011758:Pyrroles; D012277:Ricinoleic Acids; C005235:methyl ricinoleate