Synthesis of azido analogues of medermycin

The synthesis of azido analogues 2a,2b of the pyrano-naphthoquinone antibiotic medermycin I has been achieved in eight steps from naphthol 8 and azido glycosyl sugar 7 in 9.3% overall yield. Key steps include the direct (BF3Et2O)-Et-. promoted C-glycosylation of naphthol 8, introduction of an acetyl group onto a bromonaphthoquinone via Stille coupling with (alpha-ethoxyvinyl)tributyltin, furofuran annulation of a naphthoquinone to a furonaphthofuran using 2-trimethylsilyloxyfuran 5 and oxidative rearrangement of a furonaphthofuran to a furonaphthopyran.