vic-Iodo Thiocyanates and Iodo Isothiocyanates. IX. A Synthesis of Penam and Other Polycyclic Β-Lactams

Abstract

Penam (4-thia-1-azabicyclo[3.2.0]heptan-7-one) and 2,3-disubstituted penams are prepared conveniently from vic-iodo isothiocyanates beginning with the facile cyclization of the latter with di -t-butyl sodiomalonates. Treatment of the resulting di -t-butyl 2-(thiazolidin-2- ylene ) malonates with trifluoroacetic acid gives t-butyl 2-thiazolin-2- ylacetate derivatives which are reduced to the corresponding thiazolidines with aluminium amalgam. Cleavage of these t-butyl esters with hydrogen chloride affords β-amino acid hydrochlorides, which are cyclized to penam and its derivatives with 1-[3-( dimethylamino ) propyl ]- 3-ethylcarbodiimide hydrochloride. The structures of the (2α,3aβ,7aβ)- thiazolidine (5) and of the tricyclic β- lactam (41) have been confirmed by X-ray crystallography.