Dithioacetals acyl anion equivalents

Dithioacetals (see also dithianes and dithiolanes) alkylation of 98 as acyl anion equivalents 75 carbanions of 87,97-102 cleavage of 14-18,98,102 desulfurization of 78 metal-catalysed coupling 127 reaction with Grignard reagents 127 reductive lithiation of 89 synthesis of 12-19,97-102 Dithioacids synthesis of 40... 

C-C BOND-FORMING REACTIONS 4.2.1 Use of sulfides, dithioacetals and orthotrithioesters 4.2.1.1 1,3-Dithianes as acyl anion equivalents... 

The reaction of aldehydes or ketones with ethane-1,2-dithiol or propane-1,3-dithiol to form 1,3-dithiolanes or 1,3-dithianes is an important reaction, as these compounds under suitable conditions are acyl anion equivalents (see Section 5.9, p. 626). These cyclic dithioacetals have been less used as protective groups, though when required are formed in high yield in the presence of boron trifluoride-etherate.138... 

Thiophilic addition of EtMgl to dithioesters leads to acyl anion equivalents that react with electrophilic reagents to yield to dithioacetals [34]. The latter compounds may be transformed into the corresponding carbonyl compounds on hydrolysis [Eq. (24)]. 

The most systematically investigated acyl anion equivalents have been the IMS ethers of aromatic and heteroaromatic aldehyde cyanohydrins, TBDMS-protected cyanohydrins, - benzoyl-protected cyanohydrins, alkoxycaibonyl-protected cyanohydrins, THP-protected cyanohydrins, ethoxyethyl-protect cyanohydrins, a-(dialkylamino)nitriles, cyanophosphates, diethyl l-(trimethylsiloxy)-phenyimethyl phosphonate and dithioacetals. Deprotonation di these masked acyl anions under the action of strong basie, usually LDA, followed by treatment with a wide varies of electrophiles is of great synthetic value. If the electrophUe is another aldehyde, a-hydroxy ketones or benzoins are formed. More recently, the acyl caibanion equivalents formed by electroreduction of oxazolium salts were found to be useful for the formation of ketones, aldehydes or a-hydroxy ketones (Scheme 4). a-Methoxyvinyl-lithium also can act as an acyl anion equivalent and can be used for the formation of a-hydroxy ketones, a-diketones, ketones, y-diketones and silyl ketones. - - ... 

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. ... 

The synthesis of a drug using a dithian as an acyl anion equivalent Dithioacetal monoxides Protected Cyanohydrins of Aldehydes... 

Among various strategies towards ulosonic acids various acylation reactions are often used. They involve alditol derivatives as convenient substrates, and diverse acyl anion equivalents. Here belongs the synthesis of KDO, developed by Shiba et al. [84], By reaction of the triflate 67 with the lithiated 68, eight carbon atoms compound 69 was obtained (Scheme 17). Removal of O-acetyl residue with subsequent NBS promoted oxidative hydrolysis of the dithioacetal moiety resulted in the formation of KDO derivative 70. 

Metalated dithioacetals are known to be useful as acyl anion equivalents. Thus, successful diastereoselective reactions have led to many applications of dithioacetals [63]. However, only a few enantioselective reactions of symmetric dithio-... 

Dithioacetal, Trithioorthoester, and Thioglycoside Activation. DMTSF provides a chemoselective reagent for dithioacetal activation in the presence of electron-rich alkenes. This bond-forming procedure complements the TiCLj mediated reaction between acetals and sUyl enol ethers demonstrated hy Mukaiyama. The generation of ketone precursors through dithioacetal carban-ion (acyl anion equivalents) chemistry further amplifies the significance of DMTSF activation. 

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