Studies to try and epimerize the C-2 centre in compound 5 using a variety of bases proved challenging. Only tert-butoxide/THF gave a reasonable ratio (2:5 = 1:1), while other bases including DBU, failed to generate any of the desired isomer. Formation of the lithium enolate (dianion) of 6 followed by protonation with a variety of compounds bearing acidic protons on either oxygen or carbon were unrewarding. ... Encouragingly, the amount of C-2 epimer 13 was found ...
