Enolization of 2-Decalones

Article abstract of DOI:10.1021/jo00251a030

It is well-known that under thermodynamic conditions 5α-3-keto steroids such as 3-cholestanone enolize predominantly toward C-2, while the 5β-isomers enolize toward C-4.It has been tacitly assumed that 2-decalones, bicyclic analogues of the steroids, show similar selectivity.In a systematic investigation of the direction of enolization of 2-decalones, 11 bicyclic ketones plus two representative steroids have been converted to the corresponding trimethylsilyl enol ethers under thermodynamic conditions.The classical generalizations have been found to be valid for trans-2-decalones and steroidally locked cis-2-decalones with an angular methyl group.Nonsteroidally locked cis-2-decalones with an angular methyl enolize in a direction opposite to that predicted.Without an angular methyl, all three types of 2-decalones enolize in the predicted manner, but with attenuated regioselectivity.Molecular-mechanics calculations have been carried out for the olefins corresponding to decalone enols.With the exception of the nonsteroidal cis compounds with an angular methyl, the calculations agree well with the experimental data.