The known enol ether (I) was dihydroxylated with OsO4 and then oxidatively cleaved to the keto formate (II) by means of Pb(OAc)4. Reformatskii reaction of (II) with (tert-butoxycarbonyl)methylzinc bromide gave hydroxyester (III). Further cyclization of (III) using trifluroacetic acid produced lactone (IV). Halogenation with iodine monochloride afforded iodopyridine (V). Then, cleavage of the methyl ether of (V) employing trimethylsilyl iodide generated the pyridone lactone (VI), which was N-alkylated with 3-(trimethylsilyl)propargyl bromide (VII), yielding (VIII). Radical annulation of (VIII) with isonitrile (IX) in the presence hexamethylditin furnished the pentacyclic system (X). Finally, removal of the N-Boc protecting group of (X) yielded the title compound.

The known enol ether (I) was dihydroxylated with OsO4 and then oxidatively cleaved to the keto formate (II) by means of Pb(OAc)4. Reformatskii reaction of (II) with (tert-butoxycarbonyl)methylzinc bromide gave hydroxyester (III). Further cyclization of (III) using trifluroacetic acid produced lactone (IV). Halogenation with iodine monochloride afforded iodopyridine (V). Then, cleavage of the methyl ether of (V) employing trimethylsilyl iodide generated the pyridone lactone (VI), which was N-alkylated with 3-(tert-butyldimethylsilyl)propargyl bromide (VII), yielding (VIII). Finally, radical annulation of (VIII) with phenyl isonitrile (IX) in the presence hexamethylditin furnished the title pentacyclic compound.