In the preceding paper, we showed that 2-amino-4,5-dihydro-3-furancarbonitriles react with α-diazo-β-keto esters such as ethyl diazoacetoacetate and ethyl diazobenzoylacetate in the presence of rhodium(II) acetate to form ethyl 2H-pyran-2-carboxylate [1]. In continuation of this study, we examined the reactions of 2-amino-4,5-dihydro-3-furancarbonitriles (1 and 3) with dimethyl diazomalonate [2] and diethyl diazomalonate [3].When a mixture of 2-amino-4,5-dihydro-3-furancarbonitrile 1 [4], dimethyl diazomalonate, and a catalytic amount of rhodium(II) acetate in 1,2-dichloroethane was refluxed for 1 h, an N-H insertion product, dimethyl [(3-cyano-4,5-dihydro-2-furanyl)amino]propanedioate (2) was obtained in 75% yield, and the expected dimethyl 2H-pyran-2,2-dicarboxylate could not be isolated. In order to confirm the structure of 2, hydrolysis of 2 with hydrochloric acid led to tetrahydro-2-oxo-3-furancarbonitrile which was identical with an authentic sample [5]. The 1 H NMR spectrum of 2 in deuteriochloroform indicates that 2 consists of approximately a 3:2 tautomeric mixture of the enamine A and the imine B forms (Scheme 1). Abstract. 2-Amino-4,5-dihydro-3-furancarbonitriles 3 react with dialkyl diazomalonates in the presence of rhodium(II) acetate to yield dialkyl (5-amino-4-cyano-2,3-diSubsequently, to prevent the N-H insertion reaction, we investigated the reaction of 4,5-dihydro-2-pyrrolidino-, as well as of 2-piperidino-and 2-morpholino-3-furancarbonitriles 3a -h [6,7] with dialkyl diazomalonates, and found an unexpected reaction.
Rhodium(II) Acetate-CatalyzedWhen a mixture of 2-pyrrolidino-3-furancarbonitrile 3a, dimethyl diazomalonate, and rhodium(II) acetate in fluorobenzene was heated at 70 °C under nitrogen, an hydro-3-furanyl)propanedioates 4. Dehydrogenation of 4 with DDQ provided dialkyl (5-amino-4-cyano-3-furanyl)propanedioates 5.