Dithioacetals, alkylation ketene

Ketene dithioacetals are obtained in very good yield (>95%) from the disodium salt of 2-cyanoethene-l,l-dithiolate with a range of alkylating agents in the presence of tetra-n-butylammonium bromide [26]. 

Disulfides are good electrophiles for the introduction of an alkyl or arylsulfanyl group at the 2-position of 2-lithio-l,3-dithianes141,151,440. By treatment of the resulting orthoth-ioesters 265 with Lewis acids441, l,3-dithian-2-yl carbenium ions can be generated, as in the case of ketene dithioacetals with Bronsted acids439. 

Apart from the addition reaction to electrophilic olefins, the / -carbon atom of 1,1-enediamines can also substitute a,/ -unsaturated compounds carrying a leaving group. Schafer and Gewald129 have shown that 141 and 142 react with 143 to give product 144 in moderate to good yields (equation 54). Ketene dithioacetals derived from an alkyl cyanoacetate and malononitrile behave similarly to 143130. When imine 145 is employed, the reaction results in the formation of 146 (equation 55)129. Apparently displacement of ethoxy group and cyclocondensation by attack on the nitrile moiety are the key steps in the reaction. 

Oxidation of enethiolates derived from dithioesters 123 with A -sulfonyloxaziridine 117 gave the corresponding vinyl sulfenates 124. Subsequent alkylation with alkyl halides led to ketene dithioacetal A-oxides 125 in good to excellent yields (Equation 5) <2004JOC6916>. 

Acyl anion equivalents. Benzotriazol-l-ylmethyl methyl sulfide can undergo consecutive C-alkylations. The products are readily hydrolyzed with acidic aqueous methanol to give ketones. A related process involving alkylation and sulfenylation followed by treatment with a Grignard reagent to eliminate benzotriazole completes the synthesis of ketene dithioacetals. ... 

Aromatic aldehydes have been reported to undergo 1,1-addition to the ketene dithioacetal S,S-dioxides (46 R = alkyl) in either the presence or absence of benzophenone to give adducts (47). The transformation is initiated by H abstraction from the aromatic aldehyde by the n,K excited state of the sensitizer or substrate aldehyde to form the aroyl radical (48) as intermediate. These adducts may be useful synthetic precursors of inda-nones. 

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. 

Alkyl P-oxoalkanedithioates. The combination of H2S-Bp3.0Et2 dealkylate one of the S-substituents of acyl ketene dithioacetals in refluxing dioxane. 

Dithiocarboxylic acid derivatives also provide a useful route to dithioketene acetals (another name for ketene dithioacetals).Treatment of dithiopropionic acid (376) with excess LDA (for 0-alkylation reactions... 

Khalili B, Jajarmi P, Efiekhari-Sis B, Hashemi MH (2008) Novel one-pot, three-component synthesis of new 2-alkyl-5-aryl-(fH)-pyrrole-4-ol in water. J Org Chem 73 2090-2095 Murthy SN, Madhav B, Kumar AV, Rao KR, Nageswar YVD (2009) Multicomponent approach towards the synthesis of substituted pyrroles under supramolecular catalysis using P-cyclodextrin as a catalyst in water under neutral conditions. Helv Chim Acta 92 2118-2124 Pan L, Bi X, Liu Q (2013) Recent developments of ketene dithioacetal chemistry. Chem Soc Rev 42 1251-1286... 

Ketene dithioacetal derivatives (2) are available from 2,3 4,5-di-0-isopropylidene-D>arabinose diethyl dithioacetal (1) by treatment with BuOK followed by an alkyl halide to cause in situ alkylation. On exposure to nucleophiles in the presence of a Lewis acid they undergo substitution at C-3 (rather than addition to the double bond) presumably via the carbocation (3) as shown in Scheme 1. This reaction has been used, with moderate success, to introduce a thio sugar residue and hence afford a sulphur-linked disaccharide derivative. ... 

The alkylation of O-silylated dienolates with 1,3-dithienium tetrafluoroborate shows useful y-selectivity [equation (59)]. The y-alkylated products are selectively protected 1,5-dicarbonyl compounds. Unsaturated 1,5-diketones, precursors of various heterocycles, can be prepared by the reaction of the potassium enolates of methyl ketones with acyl keten dithioacetals [equation (60)]. ... 

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