Molecules 2000, 5(7), 916-926; doi:10.3390/50700916
Article

Novel Behavior of Thiiranium Radical Cation Intermediates. Reactions of Dimethyl Disulfide with Alkenes in the Presence of Pd(OAc)2

Department of Chemical Science and Engineering, Faculty of Engineering, Kobe University, Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan
* Author to whom correspondence should be addressed.
Received: 8 March 2000; in revised form: 7 June 2000 / Accepted: 20 June 2000 / Published: 7 July 2000
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Abstract: Reaction of dimethyl disulfide (1) with cyclohexene (2a) in AcOH in the presence of Pd(OAc)2 yields trans-1-acetoxy-2-methylcyclohexane (3a). The equivalent reactions with hex-1-ene (2b) and 2-methylpent-1-ene (2c) or 1-methylcyclohex-1-ene (2d) preferentially give anti-Markovnikov and Markovnikov adducts 4 and 3, respectively, by acetoxymethylthiolation of the alkene. The Markovnikov regioselectivity 3b/4b for the reaction with 2b is higher than that for the reaction using AgOAc instead of Pd(OAc)2, which proceeds via a thiiranium ion. Addition of a polar solvent (MeCN or MeNO2) to the reactions with 2b or 2c using Pd(OAc)2 abnormally decreases the Markovnikov regioselectivity. The total yield of 3 and 4 increases with an increased concentration of AcOH. Compounds 3 and 4 are also formed and the reactions in MeCN or MeNO2 not containing AcOH. A solution of Pd(OAc)2 in 1 exhibits λmax 380 nm (log ε 3.6) assigned to the absorption of a relatively stable sulfonium salt. These indicate that the reactions using Pd(OAc)2 proceed by SN2 ringopening of a new type of thiiranium radical cations paired with −OAc via the sulfonium salts. The insensitivity of the 3/4 ratios to the reaction time at 25-60°C in the reactions with 2c-d shows the ring-opening to be controlled kinetically, but the increased ratio with reaction time at 116°C in the reaction with 2b suggests that the ring-opening is thermodynamically governed. The reaction product with 2d also undergoes a skeletal rearrangement to a thietanium radical cation to give 1-acetoxymethyl-2-methylthiocyclohexane.
Keywords: Dimethyl disulfide; Palladium (II) acetate; Acetoxymethylthiolation; Thiiranium radical cation; Regioselectivity for SN2 ring-opening; Solvent effects; Thietanium radical cation; Skeletal rearrangement

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MDPI and ACS Style

Takeuchi, H.; Takatori, J.; Iizuka, S. Novel Behavior of Thiiranium Radical Cation Intermediates. Reactions of Dimethyl Disulfide with Alkenes in the Presence of Pd(OAc)2. Molecules 2000, 5, 916-926.

AMA Style

Takeuchi H, Takatori J, Iizuka S. Novel Behavior of Thiiranium Radical Cation Intermediates. Reactions of Dimethyl Disulfide with Alkenes in the Presence of Pd(OAc)2. Molecules. 2000; 5(7):916-926.

Chicago/Turabian Style

Takeuchi, Hiroshi; Takatori, Junnichi; Iizuka, Shingo. 2000. "Novel Behavior of Thiiranium Radical Cation Intermediates. Reactions of Dimethyl Disulfide with Alkenes in the Presence of Pd(OAc)2." Molecules 5, no. 7: 916-926.

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