(E)-3-Methylthio-2-propenyl p-Tolyl Sulfone1

[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.

Synthesis of a,b-Unsaturated Aldehydes.

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).

Synthesis of a,b-Unsaturated Ketones.

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.

Related Reagents.

1,3-Dibutoxy-1-lithio-1-propene; 1-Methoxyallenyllithium; 3-(Phenylsulfonyl)propanal Ethylene Acetal.

1. (a) Ogura, K. PAC 1987, 59, 1033. (b) Ogura, K. In Studies in Natural Product Chemistry; Atta-ur-Raman, Ed.; Elsevier: Amsterdam, 1990, Vol. 6, p 307.
2. Ogura, K.; Iihama, T.; Takahashi, K.; Iida, H. BCJ 1984, 57, 3347.
3. Hirata, T.; Sasada, Y.; Ohtani, T.; Asada, T.; Kinoshita, G.; Senda, H.; Inomata, K. BCJ 1992, 65, 75.
4. Ogura, K.; Iihama, T.; Takahashi, K.; Iida, H. TL 1984, 25, 2671.
5. Ogura, K.; Iihama, T.; Kiuchi, S.; Kajiki, T.; Koshikawa, O.; Takahashi, K.; Iida, H. JOC 1986, 51, 700.

Katsuyuki Ogura

Chiba University, Japan

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