| 词条 | Thioacetal |
| 释义 |
The symmetric dithioacetals are relatively common. They are prepared by condensation of thiols or dithiols with aldehydes. These reactions proceed via the intermediacy of hemithioacetals:
Such reactions typically employ either a Lewis acid or Brønsted acid as catalyst. Dithioacetals generated from aldehydes and either 1,2-ethanedithiol or 1,3-propanedithiol are especially common among this class of molecules for use in organic synthesis.[2] The carbonyl carbon of an aldehyde is electrophilic and therefore susceptible to attack by nucleophiles, whereas the analogous central carbon of a dithioacetal is not electrophilic. As a result, dithioacetals can serve as protective groups for aldehydes. Far from being unreactive, and in a reaction unlike that of aldehydes, that carbon can be deprotonated to render it nucleophilic: R'CHS2C2H4 + R2NLi → R'CLiS2C2H4 + R2NH The inversion of polarity between R'(H)Cδ+=Oδ− and R'CLi(SR)2 is referred to as umpolung. The reaction is commonly performed using the 1,3-dithiane. The lithiated intermediate can be used for various nucleophilic bond-forming reactions, and then the dithioketal hydrolyzed back to its carbonyl form. This overall process, the Corey–Seebach reaction, gives the synthetic equivalent of an acyl anion. See also
References1. ^{{GoldBookRef |title=thioacetals |file=T06348 }} 2. ^P. Stütz And P. A. Stadler "3-alkylated And 3-acylated Indoles From A Common Precursor: 3-benzylindole And 3-benzoylindole" Org. Synth. 1977, 56, 8.{{DOI|10.15227/orgsyn.056.0008}} 2 : Functional groups|Organosulfur compounds |
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