Routes to the title compounds are described, either using the selective addition of thiols to the known 6-allylidenepenicillanic acids or by the conjugate addition of Grignard derivatives, derived from 6,6-dibromopenicillanates, to substituted acrylates and acrylamides, followed by stereoselective reduction of the remaining 6-bromo-group to produce the 6p-substituted penicillanates. The 6P-derivatives containing the acryloyl side-chain were relatively unstable and readily underwent intramolecular rearrangement to the corresponding t h iazepinones.Most penicillins in use as antibiotics bear a 6p-acylamido substituent (l), a notable exception being mecillinam (2) in which an amidine group replaces the normal substituent.' Compared to the efforts made at varying the acyl group, relatively few studies have been made at replacing the 6pamido group by other substituents, apart from the efforts of Sheehan and his group.2 The discovery of new natural p-* We thank Dr. S. G. Waley and his colleagues, Sir

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Aus dem Dibromid (I) werden entsprechend dem Formelschema die Säuren (V) und (VII) dargestellt [Diskussion des konformativen Einflusses auf Umsetzung B), vgl. (IVa)‐(VI) und (Vb) ‐+ (VIIa), sowie des Mechanismus der HCl‐Eliminierung in den Folgeprodukten von (VI) zum E‐Isomeren (VIIb) bzw. zum Z‐Isomeren (VIIc)].

Ausgehend von der Reaktion zwischen dem Diazoester (I), den Phenylseleniden (II) bzw. (III) und dem Thiol (IV) lassen sich die gewünschten Carbonsäuren (V) und (VIa) bzw. (VIb) synthetisieren.