Sulfur, reaction with 1-chlorobenzotriazole

Several medio are available for the intnxluction of sulfenyl groups a to carbonyl derivatives and these have been reviewed. - The most versatile procedure involves reaction of the enolate with an appropriate thiol derivative, but the preferred m od is largely dependent on the nature of the substrate employed (see below). In most instances, sulfur has been introduced in the divalent state and subsequently oxidized, although the oxidative step has been avoided by the direct introduction of sulfur at the S oxidation level. The oxidation of sulfides to sulfoxides is a trivial procedure that can be effected by a variety of reagents. Sodium metaperiodate, m-chloroperbenzoic acid and hydrogen peroxide are the most common oxidants, but r-butyl hydroperoxide, r-butyl hypochlorite, N-chlorobenzotriazole,... 

Various halogenating agents in the presence of a chiral additive have been used as oxidant systems to prepare sulfoxides (usually in low ee). Thus, the combinations iodine/water/(+)-2-methyl-2-phenylsuccinic acid [80] or N-chloroamides/chiral alcohols [81-83] gave sulfoxides with -10% ee at best. Menthyloxysulfonium salts are prepared by oxidation of sulfides in presence of menthol. They can be isolated and recrystallized, with improvement of the diastereoisomeric excess. They are interesting intermediates for the synthesis of chiral sulfoxides, which are obtained by aqueous basic hydrolysis, with inversion of configuration at sulfur. Sulfoxide may also be obtained (in lower ee) by a one-pot reaction, without isolation of the sulfonium salt. Thus, 1-chlorobenzotriazole in the presence of (-)-menthol in methylenechloride oxidizes benzyl p-tolyl sulfide into the sulfonium salt (42a) (Figure 1.3). After crystallization and hydrolysis, (-)-benzyl p-tolyl sulfoxide is afforded in 87% ee [84]. A chiral derivative of N-chlorocaprolactam has been used to prepare some sulfoxides in low ee [85]. 

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See also in sourсe #XX -- [ , ]

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