On the synthesis of cephalosporin antibiotics. Synthesis of substituted furo‐oxathiins

Abstract β‐Acetylthiomethyl‐α‐tetronic acid (4‐acetylthiomethyl‐3‐hydroxy‐2,5‐dihydrofuran‐2‐one, X) with the boron trifluoride complexes of (substituted) benzaldehyde(s) yielded 2‐aryl‐7‐oxo‐5,7‐dihydro‐4 H ‐furo[3,4‐ e ]‐1,3‐oxathiins (V). This new ring‐closure is discussed as a potential step toward a synthesis of the cephalosporin C antibiotics. The nuclear magnetic resonance spectra of the compounds V show that the long‐range spin‐spin coupling of protons “through vinyl” depends on steric factors.