Studies on the syntheses of heterocyclic compounds. Part 877. An alternative synthesis of protected (±)-thienamycin and a related compound
An alternative total synthesis of protected (±)-thienamycin (2) and an analogue is described. (±)-4β-(2,2-Dimethoxyethyl)-3α-[(1R*)-1-(p-nitrobenzyloxycarbonyloxy)ethyl]azetidin-2-one (5), prepared from isoxazoline derivatives (4), was converted into the 2-(p-nitrobenzyloxycarbonylamino)ethyl (12) and phenyl (13) thioester phosphoranes. Intramolecular Wittig reaction of (12) and (13) produced the corresponding carbapenems (2) and (3) in poor yield. Effective transformation of (5) into the p-nitrobenzyl-protected thienamycin derivative (2) and the analogue (3) was achieved employing a carbene insertion reaction and subsequent introduction of the sulphide moiety.