Carbohydrate chemistry, nucleophilic substitution

Since the pioneering work of Karl Freudenberg on displacements of carbohydrate p-toluene-sulfonates [1-5], bimolecular nucleophilic substitutions became one of the most employed and useful reactions in carbohydrate chemistry. Indeed SN2-type reactions have allowed the introduction of a variety of heteroatoms (halogens, N-, O-, S-) into carbohydrates, and the resulting compounds have been used in many synthetic and biological contexts [6],... 

The reagent tris(dimethylamino)sulfonium difluorolrimcthylsilicate [TASF(Me)], which is commercially available, albeit expensive, has recently found application in carbohydrate chemistry as a source of nucleophilic fluoride for the substitution of triflates. For example,... 

By contrast, the use of allyltins /3-substituted by an electron-withdrawing group represents a particularly attractive option, due to their enhanced reactivity towards nucleophilic carbon radicals. For this purpose several allyltins were prepared with amide, ester, chloride, nitrile, trimethylsilyl and sulfones functionalities [292]. They have been used for the synthesis of 1,4-dienes [293] or 10-15 membered a-methylene lactones [294], in aminoacids [295] or carbohydrate chemistry [296]. The /3-functionalization by nonactivating alkyl groups is tolerated as well and was used in the synthesis of prostaglandins [297] or /3-lactams [298]. This was also applied to radical cascade reactions with up to four elementary steps with an excellent diastereoselectivity control (Scheme 6.34) [299]. 

Biochemistry is carbonyl chemistry. Almost all metabolic processes used by living organisms involve one or more of the four fundamental carbonyl-group reactions. For example, the digestion and metabolic breakdown of all the major classes of food molecules—fats, carbohydrates, and proteins—take place by nucleophilic addition reactions, nucleophilic acyl substitutions, a substitutions, and carbonyl condensations. Similarly, hormones and other crucial biological molecules are built up from smaller precursors by these same carbonyl-group reactions. 

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