104173-90-2Relevant academic research and scientific papers
Solvolyses of 17-(Tosyloxy)androstanes in Hexafluoroisopropyl Alcohol - An Example for Extreme Reactivity Differences Without the Occurence of Nonclassical Intermediates
Schneider, Hans-Joerg,Becker, Norman
, p. 74 - 82 (2007/10/02)
Solvolysis in hexafluoroisopropyl alcohol of 17α-(tosyloxy)androstane as well as of the corresponding 18-norsteroid proceeds faster than that of the 17β-isomers by a factor of >104 (25 deg C), and also considerably faster than that of cyclopentyl or cyclohexyl tosylates.The same 1,2-methyl migration products are observed with both isomers.Kinetic comparison with steroids, cyclohexane and cyclopentane derivatives with vicinal methyl groups or hydrogen shows that neither bridging with antiperiplanar C-C bonds, nor hydrogen rearrangements leading to charges at tertiary centers can be responsible for the reactivity differences.Chlorides instead of tosylates show a substantial decrease of the epimeric rate ratios.The epimers are characterized by ks/kc ratios differing by a factor of 102 to 103.Molecular mechanics calculations indicate that the fast reactions of the 17α-isomers are due to steric acceleration; the 17β-isomers react much slower than predicted by the applied force field model, which is in accord with a strong steric hindrance to solvation.Preparations of, e.g., 18-norsteroids and 13C NMR spectra are described.
