text: The Robinson synthesis is an example of a so-called relay synthesis. As many of the chemical intermediates (all steroids) were already known and available from natural resources all that was needed for a formal synthesis was proof that these intermediates could be linked to each other via chemical synthesis. Starting point for the Robinson synthesis was 1,6-dihydroxynaphthalene 1 that was converted in about 20 steps into the then already known androsterone 4. Ruzicka had already demonstrated in 1938 that androsterone could be converted into androstenedione 5  and Robinson demonstrated its conversion to dehydroepiandrosterone 6 (note the epimerized hydroxyl group) also already a known compound. Conversion of 6 to pregnenolone 7 and then to allopregnanolone 8 allowed the addition of the tail group as the acetate in 9 and then conversion to cholestanol 10. 
  The conversion of cholestanol to cholesterol was already demonstrated by oxidation of the ketone, bromination to the bromoketone and elimination to the enone.
  The conversion of cholestenone into cholesterol by the method of Dauben and Eastham (1950)  consisted of reduction of the enol acetate (lithium aluminium hydride) and fractionation with digitonin for the isolation of the correct isomer.