Rearrangements of steroids

The reactions of 6-substituted -3β,5-diacetoxy-5α-cholestane with BF₃-etherate in acetic anhydride have been investigated. The 6-substituent has been found to be important in determining which products are formed. Added acetic acid was found to have a marked effect on the relative yields of the products of the reaction of the 6β-acetoxy compound (2c) with the BF₃-etherate in acetic anhydride. The effect of 5,6-epoxy- 5α, 6β-diacetoxy- and 4,5-epoxy- functions on the reaction of steroidal 3-β-toluene sulphonate esters with Li₂CO₃-DMF and collidine has been studied. Products of direct elimination or substitution and, for the 4,5-epoxy and 5α,6β-diacetoxy compounds, rearrangement followed by elimination or substitution were isolated. In particular the 4,5-epoxy-3-tosylates give the rearranged diene-ether (71) as well as the repective 4,5-epoxy-cholest-2-ene (59 or 60). Trienes (69 and 70) are formed by the rearrangement of the Δ²-4,5-epoxides under the reaction conditions. The presence of an epoxide function adjacent to a double bond was found to give rise to an absorption maximum with an associated Cotton Effect above 200nm. In a number of 3,5,6-oxygenated cholestanes peaks assigned to C⁴-protons were observed in the NMR spectrum, and substituent shift effects on these protons and on the C⁶-,C¹⁹- and C¹⁸- protons are reported