Studies on conformation and reactivity—V : A nuclear magnetic resonance study of 4-ethylthio-4-en-3-oxo steroids and their analogs: The unique deshielding effect of a polar thio-function

Abstract A doublet centered at τ 6·22 in the NMR spectra of 4-ethylthiocholest-4-en-3-one, 17β-acetoxy-4-ethylthioandrost-4-en-3-one, 16α,17α,-epoxy-4-ethylthiopregn-4-ene-3,20-dione, and 17α-hydroxy- and 17α-acetoxy-4-ethylthiopregn-4-ene-3,20-diones, is observed and is attributed to one half of an AB-type quartet ( J = 14·5 c/s) resulting from the 6-methylene protons. The unusually large downfield shift of the doublet assigned to the C06 equatorial proton is presumed to be due to the deshielding effect of the ethylthio function at C-4. The chemical shift of the 6α-proton in cholest-4-en-3-one and its 4-substituted analogs, Me, OH, OMe, OAc, Cl, Br, SH, SAc, S-S-bis and S-bis, are tabulated and the deshielding effect of alkylthio group is found to be more than 1 ppm which is the srongest among these various functions. The unique deshielding effect of alkylthio function is shown to be general by examination of 2-ethylthio-3,5,5-trimethylcyclohex-2-enone and its 2-substituted analogs. An anomalously weak deshielding effect by the SH group on a double bond is pointed out.