Strategies for ansamycin antibiotics. Asymmetric synthesis of the C(3)- C(21) subunit of herbimycin A

Article abstract of DOI:10.1016/S0040-4020(98)01163-6

The asymmetric synthesis of 25, which constitutes the C(3)-C(21) segment of the stereochemically complex ansa chain of herbimycin A (2) has been achieved. The approach features the furan-hydropyran transformations 7→5 and 8→6 and the fragment coupling of 5 and 6 to produce the trisubstituted alkene 4 with high stereoselectivity. Stereoselective addition of the aryl anion derived from 24, which possesses the novel BIPSOP protecting group for the primary amine function, to the lactol 22 then delivered 25 as the major product.