Stereoselective synthesis of trans-benzo[d]oxazolyl)phenyl substituted β-lactams decorated with C-3 thio/seleno rich motifs: synthetic intermediates for diverse heterocycles

Herein, we reported an effectual protocol for the stereoselective synthesis of novel C-3 thio/seleno substituted ortho-, meta- and para-(2-benzo[d]oxazolyl)phenyl-β-lactams 7a-i. The reaction was performed by utilizing different S/Se-alkyl/aryl substituted acids 6a-d and isomeric ortho-, meta- and para-(2-benzo[d]oxazolyl)phenyl Schiff’s bases 3a-c and afforded exclusive formation of trans-β-lactams. The trans configuration was assigned with respect to coupling constant values of C3-H and C4-H (J = 1.4 to 2.6; C3-H and C4-H). The structure elucidation of all the thio/seleno anchored β-lactams 7a-i was performed using various spectroscopic techniques viz. FT-IR, NMR (¹H, ¹³C, and ¹³C DEPT–135), 2D-NMR (¹H–¹H COSY and ¹H–¹³C HSQC), elemental analysis (CHN), and mass spectrometry (ESI-MS). Further, divergent substrate scope accompanied by plausible mechanistic investigation have been also described. Stereoselectivity, good functional group tolerance and excellent yield along with wider synthetic utility bestows advantages to the present protocol.