3- Aminofurans, structure

The substituted 3-aminofurans (91, R = H, Me) resinify in air, can be diazotized (structure 91), and are easily hydrolyzed (structure 92 ). ° The infrared spectra of both 2- and 3-acctamidofuran show a strong NH stretching band indicating that these compounds do, indeed, exist in the acetamido form. ... 

This chapter, covering the literature of the period 1995-2006, surveys the structure of furans and their benzo derivatives in continuation of chapter 2.05 of CHEC-II(1996) <1996CHEC-II(2)259>. A fairly recent review of, mostly synthetic, furan chemistry also contains a useful bibliography of spectroscopic data <2001SOS(9)183>. Structural aspects are included in a recent review of aminofurans <2006AHC1>. 

Two alternative routes to y-keto-nitriles 10 that have been used to generate unusual 2-aminofuran derivatives are noteworthy. Treatment of the isoquinolinedi-one-glyoxal products 13 with malononitrile and diethylamine in alcoholic solvent gave the furans 15 via the intermediates 14. The 5-methyl derivative tautomerises to the product 16 (m.p. 224 °C), which was isolated in low yield. The 2-phenyl derivative cyclises to the tetracyclic product 17 whose structure was confirmed by X-ray crystallography (85CPB2663) (Scheme 2). 

Dimethyl-3-aminofuran gives a crystalline adduct (29%) (Ci3H1502N) upon treatment with benzaldehyde in aqueous ethanol. The structure of this additional product has not been established (37JA2525). 

Volume 92 of Advances in Heterocyclic Chemistry commences with a survey of 2- and 3-aminofurans authored by C. A. Ramsden (Keele University, UK), and V. Milata (Slovak University of Technology, Bratislava). The review concentrates on the synthesis and properties of furans with primary amino groups these highly reactive structures are unstable unless substituted with electron-withdrawing groups. 

Recently, Tu, Li, and coworkers [58] described the first domino [4-1-1]/ [3- -2- -l]/[5- -l] and double [4-1-3] cyclization reactions of o-phthalaldehyde 94 and 4-hydroxy-6-methyl-2H-pyran-2-one 95 with N-substituted enaminones 57 (Scheme 12.37). Using N-substituted 3-aminocyclohex-2-enones as enaminone led to pentacyclic pyrano[3, 2 2,3]indeno[2,l-c]pyridines 96 in 44-68% yield, whereas by employing N-substituted 4-aminofuran-2(5H)-ones the reaction occurred in another direction to form multifunctionalized pentacyclic pyrano[4,3- j]oxepines 97. This work provides an attractive strategy for the construction of structurally diverse pentacyclic oxa-azaspiro and oxa-azabridged skeletons. 

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