Abstract:
The synthesis of bis-spiroacetal (15) bearing an hydroxymethyl group at C-2 is described establishing a methodology for preparation of the polyether antibiotics salinomycin and narasin. Formation of an important iodohydrin intermediate has been accomplished by a highly efficient reaction of an epoxide with LiI catalysed by BF3.Et2O in THF. Displacement of the resulting neopentyl iodide was achieved in high yield by reaction of the iodide with potassium superoxide in dimethylsulphoxide/tetrahydrofuran in the presence of 18-crown-6. The synthesis of bis-spiroacetal (15) has been achieved the following sequence.