Abstract
AbstractMethyltrans‐2‐hexadecenoate (1b) on allylic bromination with N‐bromosuccinimide (NBS) (0.5 mole) yielded methyl 4‐bromo‐trans‐2‐hexadecenoate (2b) in 50% yield. Reaction with 2.0 moles of NBS afforded the allylic bromide (2b, δ 80%) as well as the dibromide (3b). Alkaline hydrolysis of the bromo ester (2b) yielded 4‐hydroxy‐trans‐2‐hexadecenoic acid (4a, δ 70%) and an unexpected product, 4‐oxo‐hexadecanoic acid (5a, δ 30%). A mechanism involving rearrangement is proposed to account for this unusual product. The effect of the ester carbonyl adjacent to the double bond in2b was found to suppress dehydrobromination (elimination) reaction and favors only substitution (SN2), unlike the allylically brominated derivatives of internal olefinic compounds. The CrO3‐pyridine oxidation of4b yielded the corresponding unsaturated ketone (7b). The structures of individual reaction products were established by elemental analyses as well as by spectral studies.
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