Olivanic acid analogues. Part 8. Halogenation and sulphenylation reactions leading selectively to cis-carbapenem precursors; stereospecific synthesis of (±)-6-epithienamycin
Introduction of halogen or sulphenyl substituents at C-7 of ketone 1, followed by stereospecific reduction steps, provides a selective route either to the (6RS,7RS,9RS) isomer 11 or to the (6RS, 7RS, 9SR) isomer 14 of 7-(1-hydroxyethyl)-8-oxo-3-oxa-1-azabicylo[4.2.0]octane-2-spirocyclohexane. The synthetic utility of chloride 6 is illustrated by its transformation to (±)-6-epithienamycin 25, and to the C-6 epimers of a (±)-6-chloroolivanic acid analogue 39.