Efficient two-step sequence for the synthesis of 2,5-disubstituted furan derivatives from functionalized nitroalkanes: successive Amberlyst A21- and Amberlyst 15-catalyzed processes.

The nitroaldol reaction of ketal-functionalized nitroalkanes with alpha-oxoaldehydes, promoted by Amberlyst A21, followed by acidic treatment (Amberlyst 15) of the obtained nitroalkanol, leads to the formation of 2,5-disubstituted furans in good yields. The procedure was successfully applied to the total synthesis of 1-benzyl-3-(5'-hydroxymethyl-2'-furyl)-indazole (YC-1), an important pharmaceutical target.