Semi-pinacol strategy for constructing B-ring of pradimicin–benanomicin antibiotics

Semi-pinacol cyclization of compound 8, having an acetal and an aldehyde substituent, was achieved by employing SmI2 and BF3·OEt2, leading to the highly stereoselective formation of cyclized product 9. The vicinal diol in 9 is discriminated, so as to allow selective glycosylation for the synthesis of pradimicin–benanomicin antibiotics.