Use of Microwave Heating in the Synthesis of Heterocycles from Carbohydrates

This review concerns the role of microwave irradiation in the synthesis of heterocycles starting from carbohydrates. This topic has received increasing interest owing to the wide variety of heterocyclic compounds as biologically significant chiral natural products or drugs, and products for industrial application, which cover nearly all aspects of carbohydrate chemistry. In particular, the possibility of employing microwave irradiation as a source of energy together with simple low-molecular-weight carbohydrates, as attractive chiral raw materials, has led to the production of low-cost and eco-friendly heterocycles within the framework of a green chemistry approach. Moreover, the employment of small amounts of solvents or solvent-free systems with solid supports, enables reaction completion in much shorter times under more environmentally clean conditions and preparation of the target compounds on the scale of grams, without the risk of any major hazards. The many possible combinations of skeletal, building block, and stereochemical diversity elements make this a highly attractive synthetic approach.This review covers the period from the first utilization of microwave irradiation until 2012 and includes the syntheses of (i) heterocycles linked directly or via a tether to carbohydrates, (ii) heterocycles annulated with carbohydrates, (iii) heterocycles from carbohydrates via hetero-Diels-Alder (HDAR) and Diels-Alder (DAR) reactions, or via 1,3-dipolar cycloadditions, with particular regard to the “click reaction” (CuAAC), (iv) iminosugars, and (v) 5-hydroxymethylfurfural.