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.
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 CHOS (Ms), or a toluenesulfonyl CHCHOS (Ts).