Steroids ccxciii. The methylenation of unsaturated ketones. Part i. addition of difluoromethylene to enones.

Thiol acidities and thiolate ion reactivities toward butyl chloride in dimethyl sulfoxide solution. The question of curvature in Broensted plots

“…In the deprotonation of MeC0CH2CH20C6H4N02 studied by Hupe and Wu a variety of oxygen bases were used.32 The pKa range 4.8-8 was covered by three diverse bases, AcO", C6F50", and (F3C)2C(0H)0", the range from pKa 7.7 to 10.1 by ArO' bases, that from 10 to 12 by oxime bases, ArCH=NO", and that from 12 to 16, which accounts for most of the curvature, by alkoxide bases. Our analysis suggests that the data may follow a pattern similar to that in Figure 3, i.e., an essentially linear region from pKa 4.8 to 12 (with considerable scatter caused by the use of several oxygen base families) and a second "linear" region from 12 to 16 with greater scatter caused by proximity effects and uncertainty in the data (pKa values in this region are difficult to measure in water).…”

Trimethylsilyl fluorosulfonyldifluoroacetate (TFDA): a new, highly efficient difluorocarbene reagent

“…Examples of additions of difluorocarbene to substrates as electron deficient as a,b-unsaturated carbonyl compounds are few and far between [24,25]. Therefore, studies were carried out in order to obtain comparative reactivity data for this new difluorocarbene reagent.…”

Fluorinated Carbenes

“…This method was used to cyclopropanate unsaturated ketones in ∆ 4,6 -and ∆ 1,4,6 -3-ketosteroids. [128][129][130] Other metal salts of chlorodifluoroacetate besides sodium may perform better in certain cases. 131 Early kinetic studies in aqueous solutions indicated that the decomposition produces difluorocarbene by a concerted loss of carbon dioxide and chloride ion.…”

“…Yields are generally modest, but the reaction is easy to perform (eq 16). , The reaction proceeds by loss of carbon dioxide and loss of chloride ion (eq 15). This method was used to cyclopropanate unsaturated ketones in Δ 4,6 - and Δ 1,4,6 -3-ketosteroids. − Other metal salts of chlorodifluoroacetate besides sodium may perform better in certain cases …”