The reaction of prostaglandin F2alpha (I) with tallium tri-acetate in acetic acid gives the inner ketal (II), which by trans-ketalization with BF3 and methanol is converted into the diol methyl ketal (III). Silylation of (III) with dimethyl-tert-butylsilyl chloride and imidazole in DMF yields the disilylated compound (IV), which is deacetylated with K2CO3 in methanol affording the alcohol (V). Collins' oxidation of (V) with CrO3-pyridine in methylene chloride gives the ketone (VI), which is deprotected with tetrabutylammonium fluoride in THF yielding the dihydroxy ketone (VII). Heating of (VII) at 160 C in HMPA affords 7-oxo-PGI2 methyl ester (VIII), which is finally hydrolyzed with NaOH in methanol-water.