New approach to the synthesis of 2,3-dihydrofuro[2,3-b]pyridine derivatives: double reduction and double heterocyclization of 2-(3-cyano-5-hydroxy-1,5-dihydro-2H-pyrrol-2-ylidene)malononitriles in the presence of sodium borohydride

The reaction of 2-(3-cyano-5-hydroxy-1,5-dihydro-2H-pyrrol-2-ylidene)malononitriles with an excess of sodium borohydride resulted in diastereoselective formation of 2,3-diaryl-substituted 4,6-diamino-2,3-dihydrofuro[2,3-b]pyridine-5-carbonitriles. This process was accompanied by opening of the pyrrole ring in the starting compounds, followed by a double reduction and tandem closure of furan and pyridine rings.