This article describes the stereoselective synthesis of monocyclic cis-β-lactams. The 2-(4-chlorophenoxy)-acetic acid or 2-phenoxy-acetic acid with a carboxylic acid activator 2-ethoxy carbonyl DCPN generate ketene in situ, which reacts with imines derived from substituted tetralone carbaldehyde yielded monocyclic cis-β-lactams having 5-methyl-1,3,4-thiadiazole-2-thiol moiety through[2+2] cyclo-addition reaction (Staudinger reaction). All structures of cisβ-lactams were elucidated by a spectral technique like FT-IR, 1 H and 13 C NMR spectra, HRMS, and single X-ray crystallography. The cis configuration of the β-lactams was determined based on coupling constant (J) value using 1 H NMR for hydrogens H-3 and H-4 of the β-lactams ring. This work presents the synthesis of β-lactams more simply with high yields. The products were simply purified by crystallization technique.