Studies on the Synthesis of Furan Compounds. XXX. Syntheses and Steric Configurations of 3-(5-Nitro-2-furyl)-2-(5-bromo-2-furyl)acrylic Acid and Its Related Compounds

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Abstract
Cis- and trans- 3-(5-Nitro-2-furyl)-2-(5-bromo-2-furyl)acrylic acids (II and III) and their functional derivatives have been synthesized in connection with the syntheses and steric configurations of 3-(5-nitro-2-furyl)-2-(5-bromo-2-furyl)acrylonitrile and its related compounds. The treatment of cis-3-(5-nitro-2-furyl)-2-(2-furyl)-acrylic acid (I) with bromine in refluxing carbon tetrachloride afforded a 1 : 1 mixture of II and III in quantitative yield. II and III afforded methyl (IV and VI) and ethyl (V and VII) esters, via each acid chloride (VIII or IX) by treatment with methanol and ethanol, respectively. Similarly, cis- and trans-3-(5-nitro-2-furyl)-2-(5-bromo-2-furyl)acrylamides (X and XI) were obtained by treatment of VIII and IX with dry ammonia in benzene. Isomerization was observed in the conversion of X into trans-3-(5-nitro-2-furyl)-2-(5-bromo-2-furyl)acrylonitrile (XII) upon treatment with phosphoryl chloride, while XI maintained its configuration under similar conditions to afford XII. On the other hand, cis-acid and esters (II, IV, and V) were converted into the corresponding trans isomers (III, VI, and VII) respectively, by treatment with hydrazine hydrate in refluxing methanol. II was confirmed to be isomerized to III by heating with hydrochloric acid or by irradiation with ultraviolet light (406 mμ). The structures and configurations of these compounds were discussed on the basis of their IR and NMR spectra.