Synthesis of some new isoxazolylacetic acid derivatives

(3-Chloroisoxazol-5-yl)acetic acid 1, a known acylating agent, useful for the synthesis of semi-synthetic cephalosporins was synthesized by a new route. Several α-substituted 3-chloroisoxazolylacetic acids 9a, b; 10a, b and 15, potential acylating agents for semi-synthetic β-lactams, were also prepared. The (E)and (Z)-3-chloro-α-methoxyiminoisoxazol-5-ylacetic acids 10a, b were separated and their structures unambiguously determined by 1H NMR spectroscopic and X-ray measurements.