Alkoxycarbenium ion pools

Alkoxycarbenium ion pool 26 was allowed to react with allyltrimethylsilane as a carbon nucleophile to give the corresponding allylated product 27. The success of the nucleophilic reaction also indicated the presence of the alkoxycarbenium ion in relatively high concentration in the solution. 

The alkoxycarbenium ions generated by the cation pool method react with various carbon nucleophiles such as substituted allylsilanes and enol silyl ethers to give the corresponding coupling products in good yields. It should be noted that the reactions of alkoxycarbenium ion pools with such nucleophiles are much faster than the Lewis acid promoted reactions of acetals with similar nucleophiles. A higher concentration of the cationic species in the cation pool method seems to be responsible. 

Generation of Alkoxycarbenium Ion Pools by Oxidative C-S Bond Cleavage... 

The a-phenylthioether 28 was oxidized in the absence of a nucleophile by low temperature electrolysis (Scheme 15). The corresponding alkoxycarbenium ion pool 26 was formed, which exhibited a single set of signals in H and l3C NMR spectroscopy. The chemical shifts were quite similar to those obtained by the oxidative C-Si bond dissociation described in the previous section. Subsequently, the cation pool was allowed to react with allyltrimethylsilane to obtain the allylated product 27. 

We chose to study the generation of alkoxycarbenium ion 26 from thioacetal 28. The electrochemically generated ArS(ArSSAr)+, 37 which was well characterized by CSI-MS, was found to be quite effective for the generation of alkoxycarbenium ions, presumably because of its high thiophilicity (Scheme 17). The conversion of 28 to 26 requires 5 min at -78 °C. The alkoxycarbenium ion pool 26 thus obtained exhibited similar stability and reactivity to that obtained with the direct electrochemical method. The indirect cation pool method serves a powerful tool not only for mechanistic studies on highly reactive cations but also for rapid parallel synthesis. 

Alkoxycarbenium ion pools can also be generated by oxidative C-C bond dissociation. Oxidative C-C bond dissociation is well known in the literature.38 Thus, the electrochemical oxidation of l,2-dimethoxy-l,2-diphenylethane 32... 

S. Suzuki, K. Matsumoto, K. Kawamura, S. Suga, and J.-I. Yoshida, Generation of alkoxycarbenium ion pools from thioacetals and applications in glycosylation chemistry, Org. Lett., 6 (2004) 3755-3758. 

Generation of alkoxycarbenium ion pools by oxidative C—S bond cleavage... 

Alkoxycarbenium ion pools can also be generated by electrochemical oxidative C—S bond dissociation (Scheme 5.20). " Arylthio (ArS) groups are known to also serve as effective electroauxiliaries for the electrochemical oxidation of heteroatom compounds. " The introduction of an ArS group decreases the oxidation potential and the C—S bond... 

Suga S, Matsumoto K, Ueoka K et al (2006) Indirect cation pool method. Rapid generation of alkoxycarbenium ion pools from thioacetals. J Am Chem Soc 128 7710-7711... 

Suzuki S, Matsumoto K, Kawamura K, Suga S, Yoshida J (2004) Generation of alkoxycarbenium ion pools Irom thioacetals and applications to glycosylation chemistry. Org Lett 6 3755-3758... 

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