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Tipson–Cohen reaction
The Tipson–Cohen reaction is a name reaction first discovered by Stuart Tipson and Alex Cohen at the National Bureau of Standards in Washington D.C. The Tipson–Cohen reaction occurs when two neighboring secondary sulfonyloxy groups in a sugar molecule are treated with zinc dust (Zn) and sodium iodide (NaI) in a refluxing solvent such as ''N'',''N''-dimethylformamide (DMF) to give an unsaturated carbohydrate.
==Background==
Unsaturated carbohydrates are desired as they are versatile building blocks that can be used in a variety of reactions.〔 For example, they can be used as intermediates in the synthesis of natural products, or as dienophiles in the Diels-Alder reaction, or as precursors in the synthesis of oligosaccharides. The Tipson–Cohen reaction goes through a ''syn'' or ''anti'' elimination mechanism to produce an alkene in high to moderate yields. The reaction depends on the neighboring substituents. A mechanism for glucopyranosides and mannooyranosides is shown below.〔
File:Scheme 1 Noren Hirani.gif
Scheme 1: ''Syn'' elimination occurs with the glucopyranosides. Galactopyranosides follows a similar syn mechanism.〔 Whereas, ''anti'' elimination occurs with mannopyranosides.〔 Note that R could be a methanesulfonyl CH2O2S (Ms), or a toluenesulfonyl CH3C5H4O2S (Ts).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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