Reactions of Carbohydrates

This chapter is divided into two parts The first and major portion is devoted to carbohydrate structure You will see how the principles of stereochemistry and confer matronal analysis combine to aid our understanding of this complex subject The remain der of the chapter describes chemical reactions of carbohydrates Most of these reactions are simply extensions of what you have already learned concerning alcohols aldehydes ketones and acetals... 

Before the widespread availability of instrumental methods the major approach to structure determination relied on a battery of chemical reactions and tests The response of an unknown substance to various reagents and procedures provided a body of data from which the structure could be deduced Some of these procedures are still used to supple ment the information obtained by instrumental methods To better understand the scope and limitations of these tests a brief survey of the chemical reactions of carbohydrates is m order In many cases these reactions are simply applications of chemistry you have already learned Certain of the transformations however are unique to carbohydrates... 

Cleavage reactions of carbohydrates also occur on treatment with aqueous base for prolonged periods as a consequence of base catalyzed retro aldol reactions As pointed out m Section 18 9 aldol addition is a reversible process and (3 hydroxy carbonyl com pounds can be cleaved to an enolate and either an aldehyde or a ketone... 

Generally speaking, the phosphorylated deoxysugars undergo the usual reactions of carbohydrates without complication. For instance, both 2-deoxy D-ribose 5-phosphate (52, 59) and 2-deoxy D-xylose 5-phosphate (2) can be reduced to the corresponding 2-deoxy d-erythro- (48) and 2-deoxy D-threo-pentitol 5-phosphates (49). 2-deoxy ribose 5-phosphate has also been oxidized (52) to the corresponding phosphorylated acid (50). 

Electron-transfer reactions occur all around us. Objects made of iron become coated with mst when they are exposed to moist air. Animals obtain energy from the reaction of carbohydrates with oxygen to form carbon dioxide and water. Turning on a flashlight generates a current of electricity from a chemical reaction in the batteries. In an aluminum refinery, huge quantities of electricity drive the conversion of aluminum oxide into aluminum metal. These different chemical processes share one common feature Each is an oxidation-reduction reaction, commonly called a redox reaction, in which electrons are transferred from one chemical species to another. 

Scheme 3.43. Samarium(ll) iodide-promoted domino reaction of carbohydrates.

Although reaction of carbohydrates with such activated alkenes as acrylonitrile and methyl vinyl sulfone has industrial importance, the... 

The reaction of carbohydrates with sulfuryl chloride was first studied by Helferich and coworkers,68 70 and the work was extended by J. 

Applying the coupling conditions established by Guillaumet et al.,n9 Leconte et al. have developed the coupling reaction of carbohydrate-connected benzylsulfanyl OZTs with boronic acids and stannanes in good yields (Scheme 63).122... 

Study of the photochemical reactions of carbohydrates is a topic of longstanding interest among chemists in fact, publications on this subject first appeared shortly after the beginning of the present century. Much of the early work in this area was concerned with changes, in the physical properties of reaction mixtures, arising from irradiations conducted under various conditions. Relatively little identification of the photoproducts was undertaken prior to the introduction of modem instrumentation. 

The purpose of the present article is to review comprehensively those photochemical reactions of carbohydrates for which product structures have been established, and to apply current mechanistic reasoning to the understanding of these reactions. Two reviews of carbohydrate photochemistry already exist. The first1 2 was published in this Series in 1963, prior to the considerable recent growth in this field, and the second was a brief summary published in the Japanese literature in 1973. 

An organizational plan based upon the type of functional group has been adopted here in presenting and discussing the photochemical reactions of carbohydrates. 

Three types of photochemical reaction of carbohydrate acetals have been investigated. Early studies centered on the photochemical fragmentation of phenyl glycosides, and the photolysis of o-nitrobenzyli-dene acetals. (The latter reactions will be discussed with the photolysis of other nitro compounds see Sect. VII,1.) Later experiments were concerned with hydrogen-abstraction reactions from acetal carbon atoms by excited carbonyl compounds. 

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