Synthese von 3,3a-Dihydro-2H,5H-azeto[2,1-b]benzo[d]1,3-oxazin-2,5-dionen, 2. Mitt.

Starting from the thioformimidates4 a, b, c and substituted acetylchlorides, the 3R*/4S* 4-methylthio-2-azetidinones5, 13 a, b, c are synthesized.5 is dehalogenated to6. Debenzylation of6 leads to7 and10, which undergo ring closure to9 and12 by the action of chlorine inDME. Hydrazinolysis of13 a, b, c and acylation of the intermediates14 a, b, c afford15 a, b, c. Removal of the protective groups leads to16 d, e, f. The diastereomeric mixtures17 d, e, f, which are obtained by the chlorolysis of16 d, e, f, undergo ring closure to the 3R*/4S* isomers of the title compounds18 d, e, f either spontaneously or by action of silvertetrafluoroborate/silveroxide. Chlorolysis of19 yields the diastereomeric mixture20. Treatment of20 with silvertetrafluoroborate/silveroxide gives21 and22.

Herrn Professor Dr.Hermann Bretschneider zum 80. Geburtstag gewidmet.