[92610-41-8] · C11H14O2S2 · (E)-3-Methylthio-2-propenyl p-Tolyl Sulfone · (MW 242.39)
(a synthetic reagent for preparation of a,b-unsaturated aldehydes and ketones)
Alternate Names: MTPTS; (E)-1-methylthio-3-(p-toluenesulfonyl)-1-propene.
Physical Data: colorless crystals; mp 79-80 °C (from EtOH).
Solubility: sol DMF, CHCl3; slightly sol MeOH, EtOH, diethyl ether, CCl4; practically insol H2O, hexane.
Preparative Methods: either by the reaction of sodium methanethiolate or dimethyl sulfide with 3-chloro-1-propenyl p-tolyl sulfone2 or by a-selenylation of 3-(methylthio)propyl p-tolyl sulfone and subsequent oxidative dehydroselenylation.3
Handling, Storage, and Precautions: very stable at ambient temperature. Use in a fume hood.
Monoalkylation of MTPTS can be achieved by treatment with an alkyl halide in the presence of Potassium Hydroxide-TOMAC (a phase-transfer catalyst) or Sodium Hydride in DMF.4 The reaction of the monoalkylation product with Titanium(IV) Chloride and Copper(II) Chloride in acetic acid-water followed by treatment with Potassium Carbonate in DME affords a,b-unsaturated aldehydes (eq 1).
The second alkylation of MTPTS also occurs regiospecifically at the carbon a to the sulfonyl group. Since the dialkylated product is sensitive to silica gel, the reaction mixture is subjected without purification to hydrolysis with TiCl4 and CuCl2 in acetic acid-water to yield directly the corresponding b,b-disubstituted a,b-unsaturated aldehyde (eq 2).
The dialkylated MTPTS undergoes a facile 1,3-rearrangement of its sulfonyl group on silica gel and a thermodynamically stable 2-alkenal dithioacetal S,S-dioxide is produced.5 Since it has an active proton, the rearrangement product can be further alkylated. Subsequent hydrolysis of the alkylated product with CuCl2 in methanol-water produces a,b-unsaturated ketones (eq 3). The synthetic method using MTPTS is characterized by its wide applicability to make various a,b-unsaturated ketones, three substituents of which are optionally and regiospecifically selected.
Chiba University, Japan