Ketene dithioacetals deprotonation

Ketene dithioacetals are deprotonated with LDA-HMPA and complexed with copper(l) iodide (Scheme 36). This reagent reacts with allylic halides exclusively at the y-position with allylic rearrangement (5n20. The reaction of the lithium reagent with simple alkylating reagents gives mostly a-attack. Ketene dithioacetals can be converted to esters by aqueous mercury(II) chloride. 

Reaction of the anion (243) with trimethylsilyl chloride, D2O and benzophenone, respectively, gave compounds (245), (246), and (247). Acid-treatment of (247) afforded ring-enlarged heterocycle (249) rather than the ketene dithioacetal (248), but (248) could he obtained by deprotonation of the trimethylsilyl derivative (245) with butyllithium and reaction with benzophenone <76TL1251>. 

Lithio-2-trimethylsilyl-l,3-dithiane is the most widely utilized reagent for the conversion of ketones and aldehydes to the corresponding ketene dithioacetals (Scheme 2.49) [126-128]. It is used for the synthesis of functionalized 2-alkylidene-1,3-dithianes 79 [129-135]. The 2-alkylidene-l,3-dithianes 79 thus synthesized are useful synthetic intermediates, which are conveniently accessible by means of Peterson reactions, and they can be transformed into various compounds [136, 137]. For example, compounds 79 are converted to the corresponding carboxylic acids, aldehydes, and enones by hydrolysis, hydrogenation followed by hydrolysis, and deprotonation followed by alkylation and hydrolysis, respectively (Scheme 2.49) [138-140]. 

The substituted ketene S,S-dithioacetal (76) has been developed as a P-lithioacrylate equivalent (Scheme 22). Deprotonation of (76) leads to an allylic anion (77) that reacts with a wide range of electophiles to give the T-substituted adduct (78), as the only observed product. Hydrolysis of the ketene thioacetal then releases the carboxyl residue, and this activates the system towards elimination of thiophenol, thereby unmasking the acrylate unit. Dianion (79) may also be regarded as a modified B-lithio-acrylate equivalent, but the chemistry of this species is diverse. Not only have B-substituted a, B-unsaturated amides been synthesized, but the same reagent reacts, for example, with epoxides to give ultimately dihydropyrans the species (79) is therefore perhaps more accurately represented as equivalent to the dipolar... 

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