Simple Synthesis of 3a,6a-Dihydrofuro [2,3-b]furan Derivatives via the Reaction of β-Dicarbonyl Compounds with 5-Cyano- and 5-Methoxycarbonyl-2-nitrofurans1 - Makosza, Mieczyslaw; Niyazimbetov, Marat (Synlett, 1992)