Microwave-assisted Chemistry of Carbohydrates

Antonina Corsaro, Ugo Chiacchio, Venerando Pistara, and Giovanni Romeo 

Because of new technology, microwave energy has been widely adopted as an alternative or complementary source to the thermal energy in all areas of chemistry and, particularly, in synthetic chemistry because its use provides higher yields and dramatically shorter reaction times, and sometimes it enables reactions to be conducted under solvent-free conditions or with much reduction of solvent use. 

Most arguments already treated in our previous review [3] have again been discussed in brief, but expanded with the most recent work published until July 2005. Topics include selective and nonselective protection (for example acylation, acetala- 

Microwaves in Organic Synthesis, Second edition. Edited by A. Loupy Copyright 2006 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-31452-0 

Several methods have been described for rapid and high-yielding microwave-assisted protection of carbohydrate hydroxyl functionalities with acetic anhydride, acetyl, chloroacetyl, pivaloyl, dodecanoyl, and benzoyl chlorides, and with a conventional base or a resin-linked amine. The use of solid supported reagent in these reactions resulted in reactions which are slightly slower but still comparable with conventional methods. 

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A. Corsaro, U. Chiacchio, V. Pistara, and G. Romeo, Microwave-assisted chemistry of carbohydrates, Curr. Org. Chem., 8 (2004) 511-538. 

Corsaro, A. Chiacchio, U. Pistara, V. Romeo, G. 2006. Microwave-assisted chemistry of carbohydrates. In Microwaves in organic synthesis 2nd, ed. A. Loupy, Ed. Wiley-VCH Weinheim, Germany, pp. 579-614. 

With these results in hand, several examples in carbohydrate chemistry have been performed including glycosylations, peracetylations, saponifications, and epoxidations of glucose derivatives. Within 2-10 min (depending on the chemistry and the scale) 60-220 g of the desired compounds have been generated, showing the easy access of products in the multigram level by solventless microwave-assisted chemistry [37]. 

Today, these new possibilities assume an important significance because of the growing development of carbohydrate chemistry as a consequence of the change from petroleum as raw material to natural feedstocks. Growth of microwave-assisted chemistry in industry is also likely, because of the demonstrable possibility of moving from small-scale (g) to the multigram (kg) synthesis of carbohydrate derivatives known to be valuable intermediates in the synthesis of diverse natural products and their analogs. 

Microwave-assisted epoxide ring-openings of l,5 2,3-dianhydro-4,6-0-benzyl-idene-D-allitol with nucleobases have been reported [218], Various rapid microwave-assisted protection and deprotection methods in the area of carbohydrate chemistry are known [210], and two general review articles on microwave-assisted carbohydrate chemistry were published in 2004 [219, 220]. 

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