Regio- and Diastereoselective Synthesis of trans-2,3-Dihydrofuran Derivatives in an Aqueous Medium

A wide variety of fused trans-2,3-dihydrofuran derivatives were synthesized through a one-pot three-component reaction of an aromatic aldehyde, a cyclic β-diketo compound, and an in situ-generated pyridinium ylide in refluxing. The pyridinium ylide was formed from either 2-bromo-1-phenylethanone or 4-nitrobenzyl bromide and pyridine in the presence of 10 mol% of sodium hydroxide. Pyridine plays crucial role in forming the pyridinium salt, which, in turn, forms a nitrogen ylide in the presence of sodium hydroxide. The ylide assists a Michael-initiated ring-closure reaction, but is not itself incorporated in the final product. The protocol is environmentally acceptable because no organic solvent is involved at any stage. Furthermore, the method is highly diastereoselective, gives good yields, and does not involve extensive workup procedures or chromatographic separations, as the desired products can be isolated by filtration and drying.