| Dihydrofurans are an important class of heterocycles that were frequently found in awide range of biologically active natural or synthetic products. Their broad occurrence innatural or synthetic bioactive substances has stimulated significant interest in thedevelopment of new and efficient preparation methods. In recent years, multicomponentreactions have been extensively studied because of their simple operation, good efficiencyand sometime, an excellent atom economy. Multicomponent reaction was often used in aone-pot synthesis of a complex molecule starting from three or more simple substrates,providing a powerful tool towards the rapid construction of diverse and complexheterocyclic compounds.A multicomponent protocol for controllable synthesis of2,4-diacyl-2,3-dihydrofuranderivatives was presented in this paper. The reaction was triggered by a Knoevenagelcondensation of1,3-dicarbonyl compound with formaldehyde, which generated a2-methylene-1,3-dicarbonyl intermediate that can be trapped by phenacylpyridinium saltthrough [4+1] annulation reaction. Unexpectedly, under suitable conditions, theannulation products underwent a hydroxymethylation to afford hitherto unreported2,4-diacyl-2-hydroxylmethyl-2,3-dihydrofurans in good yields. By means of carefullyselecting the reaction parameters, such as solvent, base and temperature, we are able tocontrol the reaction selectivity to obtain either Knoevenagel/[4+1] annulation orKnoevenagel/[4+1] annulation/hydroxymethylation products. In addition, thedownstream use of the obtained2,3-dihydrofurans in synthesizing some valuable organicmolecules was also explored.In conclusion, a three-component reaction of phenacylpyridinium salt,1,3-dicarbonylcompound and formaldehyde not only enabled us to realize a controllable synthesis ofdihydrofurans with eco-friendly method, but also opens an avenue to access hithertounreported2,4-diacyl-2-hydroxylmethyl-2,3-dihydrofurans. |
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