Navigation

0 Hits

  • Previous / Next

You are using Science Of Synthesis as a Guest.
Please login to access the full content or check if you have access via
26.4.2.1.2.1 Variation 1: Of Ketones

DOI: 10.1055/sos-SD-026-00532

Landais, Y.; Vincent, J. M.Science of Synthesis, (200526701.

Sulfoxides and dicyclohexylcarbodiimide react under acid catalysis with active methylene compounds such as ketones and 1,3-diketones to give oxo sulfonium ylides, e.g. 5,5-dimethylcyclohexane-1,3-dione (dimedone, 263) on treatment with dimethyl sulfoxide/dicyclohexylcarbodiimide gives 2-dimethyl-λ4-sulfanylidene derivative 265 (Scheme 63).[‌349‌‌351‌] The formation of 265 is likely to proceed through the nucleophilic attack of the enol form of the activated methylene compound 263 onto a dimethyl sulfoxidedicyclohexylcarbodiimide adduct of type 266 [R1=C(NHCy)=NCy]. Loss of a proton then occurs spontaneously in this very polar medium to provide the ylide 265.[‌351‌] Dimethyl sulfoxide is generally used but other sulfoxides are also employed with similar results. Several acids catalyze the reaction but anhydrous orthophosphoric acid affords the best results.[‌351‌] The synthesis of sulfonium ylides is also carried out using the dimethyl sulfoxideacetic anhydride system, which tends to be less reactive than the dimethyl sulfoxidedicyclohexylcarbodiimide system.[‌350‌,‌351‌] This transformation is however restricted to methylene groups activated by electron-withdrawing groups such as carbonyls, nitriles, or phosphates. Several variations around this theme are available, based on the modification of the nature of the adduct 266. For example, the CoreyKim reagent 264[‌352‌] prepared by reaction of N-chlorosuccinimide with dimethyl sulfide reacts very efficiently with active methylene compounds such as 263 to afford the corresponding sulfonium ylide 265 in excellent yield.[‌353‌] It is noteworthy that the use of a large excess of this reagent with γ-hydroxycarbonyl compounds yields directly the sulfonium ylide through a β-dicarbonyl intermediate;[‌354‌,‌355‌] dimethyl sulfoxide and the oxidant pyridinesulfur trioxide in the presence of triethylamine react similarly.[‌356‌] Again, an adduct such as 266 (R1=SO3) resembling 266 [R1=C(NHCy)=NCy] is proposed as the active species of this oxidation.[‌357‌]

Meeeee 88 Meeeeeeeeee ee Meeeeeeeee Meeeee Meeeee ee Meeeeeee ee Meeeee Meeeeeeee Meeeeeeee[‌888‌,‌888‌]

Meeeeeeeeeee Meeeeeeee

8-(Meeeeeee-λ8-eeeeeeeeeeeee)-8,8-eeeeeeeeeeeeeeeeeee-8,8-eeeee (888); Meeeeee Meeeeeeee:[‌888‌]

Me e eeeeeeeeee ee MMM (8.888e, 88eeee) ee eeeee MM8Me8 (888eM), MMM (8.8eM, 88.8eeee) eee eeeee eeeeeeee ee 88°M eeeee eeeee, eee eee eeeeeeee eee eeeeeeeee eee 8e ee eeee eeeeeeeeeee. Meee, e eeee ee 8,8-eeeeeeeeeeeeeeeeeee-8,8-eeeee (888; 8.8e, 88eeee) eee eeeee ee eee eeee eeeeeeeeeee. Meeee 8e, Me8M (8.8eM, 88.8eeee) eee eeeee ee eee eeeeeee, eee eeeeeeee eee eeeeeeeee eee ee eeeeeeeeee 8e ee eee eeee eeeeeeeeeee. Mee eeeeeee eee eeeeeee eeee eeee eeeee (88eM), eee eeeeeeeee eeee Me8M (888eM). Mee eeeeeee eeeee eee eeeeee eeee eeeee (8×88eM), eee eeeee (MeMM8). Meeeeee ee eee eeeeeee eee eeeeeeeeeeee ee eee eeeeeee ee eeeeee eeeeeeeeeeeeee (eeeeee eee, MMMe8/eeeeeee 88:8) eeeeeeee eee eeeee eeeeeeee; eeeee 8.88e (88%); ee 8888.8°M.

References


Cookie-Einstellungen