Both targets 2 and 3 appeared to be accessible from a common
yne-diol 6 using methodology developed by us: firstly, a silvercatalysed 5-endo-dig cyclisation38 of this diol 6 was expected to
deliver the advanced intermediate furan 4 while a similar cyclisation but induced by molecular iodine39 would result in formation of
the related iodofuran 5, which should then allow incorporation of
the final methyl group on the way to F-acid F6 3 (Scheme 1)