(1r,5s)-6-(4-Methyl-2-Oxo-2,5-Dihydrofuran-3-Yl)-3-Phenyl-4-Oxa-2,6-Diaz Abicyclo[3.2.0]Hept-2-En-7-One

Efficient large-scale and feasible industrial synthesis of the 1-oxacephem core structure from 6-aminopenicillanic acid (6-APA) has been reported for several decades. Via the industrial synthesis route, a byproduct (compound 9) containing a butenolide unit was purified and characterized by NMR and HRMS in this work. It is worth noting that compound 9 is an entirely new compound. Additionally, a plausible mechanism and effects on the formation of 9 by different Lewis acids were proposed. The discovery of compound 9 could improve the purity of this feasible industrial synthesis and provide considerable cost savings.