Studies on Ketene and Its Derivatives. LXXXV. Reactions of 4-Bromo-3-hydroxybutanoate and Its Acyl Derivatives

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Acylation of ethyl 4-bromo-3-hydroxybutanoate (I) with acetic anhydride, benzoyl chloride, diketene, and phenyl isocyanate gave rise to ethyl 3-acetoxy-4-bromobutanoate (IIa), ethyl 3-benzoyloxy-4-bromobutanoate (IIb), ethyl 3-acetoacetoxy-4-bromobutanoate (IIc), and ethyl 4-bromo-3-(N-phenylcarbamoyloxy) butanoate (IId), respectively. Reaction of IIa with sodium ethoxide in abs. ethanol gave ethyl 4-hydroxycrotonate (III) and ethyl 4-bromocrotonate (IV). The similar reaction of IIb afforded IV and 4-benzoyloxycrotonate (Vb). Similarly, IIc was converted to III, 4-acetoacetoxycrotonate (Vc), and 3-acetyl-4-ethoxycarbonylmethyltetrahydrofuran-2-one (VI). On the other hand, reaction of IId under the same condition did not give the acyl migrated product such as ethyl 4-N-phenylcarbamoyloxycrotonate (Vd) but afforded ethyl 4-anilinocrotonate (VIII).