α,β-Unsaturated Carboxylic Acid Derivatives. XI. Convenient Synthesis of tert-Butyl 2-Alkoxy- and Hydroxy-2-acetylamino-3-mono- or 3,3-dihaloalkanoates

It was found that the halogenation of t-butyl 2-acetylamino-3-bromo-2-alkenoate (3) by NBS or NCS gave t-butyl 2-acetylimino-3,3-dihaloalkanoate (6 and 7). The addition of water or several saturated, unsaturated and polyhydric alcohols to the carbon-nitrogen double bond of 6 or 7 was accomplished to give t-butyl 2-acetylamino-2-alkoxy- and hydroxy-3,3-dihaloalkanoate. Similarly, the treatment of t-butyl 2-bromoacetylamino-2-alkenoate in alcohol gave t-butyl 2-acetylamino-2-alkoxy-3-bromoalkanoate, via the addition of alcohol to the imino intermediate (2). The formation mechanism and the structural assignment are discussed.