Asymmetric synthesis sulfone electrophiles

The intramolecular cyclization of unsaturated carboxylic acids is one of the most straightforward routes to the synthesis of lactones, which leads directly to the desired products. In general, electrophilic reagents such as iodine, phenylselenium chloride, and mercuric or palladium salts promote this cyclization [26]. However, a second step is necessary to remove the reagent. Although the cyclization of unsaturated carboxylic acids promoted by a Brpnsted acid is a well-known reaction, it occurs mostly with more than stoichiometric quantities of a Brpnsted acid [27], On the other hand, it was reported that a variety of substituted y- and 5-lactones could be easily prepared from unsaturated carboxylic acids in excellent yields using trifluoromethane-sulfonic acid (TfOH) as a catalyst (Scheme 9.17) [28]. However, applications of this method, such as an asymmetric... 

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