In previous work [1], we showed that the reaction of 3-arylmethylidene-5-R-3H-furan-2-ones with malonic acid dinitrile leads to the formation of 6-amino-4-aryl-2-R-4H-furo[2,3-b]pyran-5-carbonitriles. In a continuation of a study of this reaction, we investigated the effect of substituents in the arylmethylidene fragment on the structure of the compounds formed.

The reaction of 3-(2-hydroxyphenylmethylidene)-5-R-3H-furan-2-ones 1 and 2 with malonic acid dini- trile was carried out by heating the reagents at reflux in DMSO solution in the presence of a catalytic amount of triethylamine. The reagent ratio was 1:1. The reaction led to the formation of 6-amino-5-imi- no-2-R-11bH-3,4,7-trioxacyclopenta[c]phenanthrenes 3 and 4.

No conclusion can be drawn concerning the predominance of one of the possible tautomeric forms (a or b) on the basis of the available spectral data and quantum-chemical calculation results.

The first step probably proceeds through addition of malonic acid dinitrile at the activated C = C bond of the substituted furan-2-one to give a Michael adduct. Subsequent stabilization of this adduct may occur in several ways. Pathway a involves initial participation of the hydroxyl group of the aromatic substituent, leading to formation of substituted chromenes. The reaction does not stop at this step and further reaction of the cyano group and carbonyl group of the heterocycle leads to final products 3 and 4. The possibility of formation of tetracyclic bridged products A does not realize.

Pathway b entails initial reaction of a cyano group with the carbonyl group of the heterocycle to give furopyran systems, whose stabilization also leads to final reaction products 3 and 4.

The 1H and 13 C NMR spectra were taken on a Varian-400 spectrometer at 400 and 100 MHz, respectively in CDCl3 at 20–25 °C with TMS as internal standard. Thin-layer chromatography was carried out on Silufol UV-254 plates using 2:2:1 hexane − ethyl acetate − chloroform as the eluent. The plates were developed with iodine vapor.

6-Amino-5-imino-2-R-11bH-3,4,7-trioxacyclopenta[ c ]phenanthrenes 3 and 4. Several drops of triethylamine were added to a mixture of arylmethylidene-3H-furan-2-one 1 or 2 (0.01 mol) and malononitrile (0.01 mol) in DMSO solution. The reaction mixture was heated at reflux for 4–5 h, poured into ice water, and neutralized by adding dilute hydrochloric acid. The crystals formed were filtered off and recrystallized from hexane.

6-Amino-5-imino-2-phenyl-11bH-3,4,7-trioxapenta[ c ]phenanthrene (3) was obtained in 87% yield; mp 191–193 °C. 1H NMR spectrum, δ, ppm: 4.31 (1H, s, CH); 6.52 (1H, s, =CH); 7.35–7.69 (9H, m, Ar); 7.91 (1H, s, NH); 8.92 (2H, s, NH2). 13 C NMR spectrum, δ, ppm: 25.92, 97.65, 116.55, 118.32, 119.12, 118.32, 120.45, 121.54, 125.32, 126.65, 127.67, 128.05, 128.76, 129.63, 131.76, 132.04, 132.20, 157.99, 168.95. Found, %: C 73.00; H 4.54; N 8.69. C20H14N2O3 .Calculated, %: C 72.72; H 4.27; N 8.48.

6-Amino-5-imino-2-(4-methylphenyl)-11bH-3,4,7-trioxacyclopenta[ c ]phenanthrene (4) was obtained in 89% yield; mp 197–199 °C. 1H NMR spectrum, δ, ppm: 2.34 (3H, s, CH3); 4.36 (1H, s, CH); 6.52 (1H, s, =CH); 7.35–7.69 (8H, m, Ar); 7.92 (1H, s, NH); 8.87 (2H, s, NH2). 13 C NMR spectrum, δ, ppm: 21.45, 26.56, 99.43, 114.25, 116.33, 118.43, 119.32, 122.47, 124.79, 128.65, 129.12, 129.75, 130.65, 131.36, 132.54, 134.14, 137.32, 159.06, 170.15. Found, %: C 73.57; H 4.94; N 7.68. C21H16N2O3. Calculated, %: C 73.24; H 4.68; N 8.13.

This work was carried out with the financial support of the Russian Federation President's Grant for

State Support of Young Russian Scientists No. MK-2054.2011.3 and Russian Basic Research Fund Grant 10-03-00640-a.