Carbohydrate chemistry, cycloaddition reactions

The [ 2 + 4]-cycloaddition reaction of aldehydes and ketones with 1,3-dienes is a well-established synthetic procedure for the preparation of dihydropyrans which are attractive substrates for the synthesis of carbohydrates and other natural products [2]. Carbonyl compounds are usually of limited reactivity in cycloaddition reactions with dienes, because only electron-deficient carbonyl groups, as in glyoxy-lates, chloral, ketomalonate, 1,2,3-triketones, and related compounds, react with dienes which have electron-donating groups. The use of Lewis acids as catalysts for cycloaddition reactions of carbonyl compounds has, however, led to a new era for this class of reactions in synthetic organic chemistry. In particular, the application of chiral Lewis acid catalysts has provided new opportunities for enantioselec-tive cycloadditions of carbonyl compounds. 

Giuliano R. M. Cycloaddition Reactions in Carbohydrate Chemistry. An Overview... 

Click chemistry has been particularly active in various fields this year. For example, ample applications of click chemistry have been seen in carbohydrate chemistry. Various /weiido-oligosacchardies and amino acid glycoconjugates were synthesized via an intermolecular 1,3-dipolar cycloaddition reaction using easily accessible carbohydrate and amino acid derived azides and alkynes as building blocks <06JOC364>. The iterative copper(I)-catalyzed... 

S. Dedola, S. A. Nepogodiev, and R. A. Field, Recent applications of the Cul-catalysed Huisgen azide-alkyne 1,3-dipolar cycloaddition reaction in carbohydrate chemistry, Org. Biomol. Chem.., 5 (2007) 1006-1017. 

J. C. Lopez and G. Lukacs, Pyranose-derived dienes and conjugated enals—preparation and Diels-Alder cycloaddition reactions, in Cycloaddition Reactions in Carbohydrate Chemistry, 1992, pp. 33-49. 

Another annellation reaction starts from a,a -dibromo-o-xylene, an activated olefin and zinc.63 This reaction, according to the authors proceeds by a Diels-Alder cycloaddition via the o-xylylene (Scheme 15.10), and was employed in carbohydrate chemistry to prepare anthracyclinones analogues.64 No reaction occurs without sonication. Instead of a cycloaddition, another explanation can be postulated, consisting first of addition of a mono-organozinc reagent to the activated olefin, followed by alkylation of the resulting enolate by the second benzylic bromide. 

Cycloadditions are widely used methods for carbocycle construction [352], In this context, the Diels-Alder reaction has been studied in carbohydrate chemistry. Using this approach, the sugar can be used as the dienophile or as the diene with a large preference for the former. 

For a review, see Giuliano, RM, Cycloaddition reactions in carbohydrate chemistry — an overview. In Cycloaddition Reactions in Carbohydrate Chemistry, Giuliano, RM, Ed., American Chemical Society, Washington, DC, pp. 1-23, 1992. 

Giuliano, R. M. Cycloaddition reactions in carbohydrate chemistry. An overview. ACS Symp. Ser. 1992,494,1-23. 

Microwave irradiation has been successfully applied in chemistry since 1975 and many examples in organic synthesis have been described [3, 4], Several reviews have been published on the application of this technique to solvent-free reactions [5], cycloaddition reactions [6], synthesis of radioisotopes [7], fullerene chemistry [8] and advanced materials [9], polymers [10], heterocyclic chemistry [11], carbohydrates [12], homogeneous [13] and heterogeneous catalysis [14], medicinal and combinatorial chemistry [15], and green chemistry [16]. All these applications are described elsewhere in this book. 

ChmielewskiM, KaluZaZ, Grodner J, Urbanski R (1992) In Giuliano RM (ed) Cycloaddition Reaction in Carbohydrate Chemistry. ACS Symposium Series 494 50... 

A review of cycloaddition reactions in carbohydrate chemistry is presented. The use of carbohydrate-derived dienes and dienophiles in the Diels-Alder reaction, hetero-Diels-Alder and dipolar addition reactions of carbohydrates are described. Stereochemical aspects of the cycloaddition processes are also discussed, and applications to the synthesis of natural products are included for each reaction type. Much of the material presented has appeared in the literature within the past five years however, earlier studies are also included in order to give a more representative historical perspective. 

In Cycloaddition Reactions in Carbohydrate Chemistry Giuliano, R. ACS Symposium Series American Chemical Society Washington, DC, 1992. 

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