Aldol condensation reactions of tricarbonyliron complexes. Towards building blocks for the synthesis of carbomycin B/tylosin macrolide antibiotics and fluorinated analogs

Tricarbonyliron complexes of α-methoxyheptadienone 3 and octadienone 8 were reacted as silyl enol ethers with protected β-hydroxypropanal and TiCl4, to give the syn–syn aldol condensation products 4 and 11 as major, isolated diastereomers (61 and 45%). Products 4 and 11 were converted into key intermediates of previous total syntheses of carbonolide B and tylonide, in a few steps, including the iron-directed reduction to syn diols and partial ozonolysis. The same methodology was used for the high yielding synthesis of a monofluorinated analog.