Studies of Heteroaromaticity. IX. Stability and Reactivity of 5-Nitro-2-furyl Diazo Compounds

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Abstract
(5-Nitro-2-furyl)diazomethane (2), 3-(5-nitro-2-furyl)diazopropene (4), and 1-(5-nitro-2-furyl)diazoethane (6) were prepared by the oxidation of the corresponding hydrazones with active manganese dioxide. The relative stabilities of these diazo compounds were then compared with p-nitrophenyldiazomethane in their ethanolic solutions and in their solid states by measuring their decomposition rates spectroscopically; it was found that the stability decreased in the following order: 2& 6\backsimeqp-nitrophenyldiazomethane>2\backsimeq4 & & in ethanol & p-nitrophenyldiazomethane>2>4>6 & & in the solid state. The reactivities of these diazo compounds were also investigated in the decomposition reactions; the thermal and photolytic decomposition of 2 afforded l,2-di(5-nitro-2-furyl)ethylene (7) in a low yield, but 4 cyclized readily to 3-(5-nitro-2-furyl)pyrazole (8) in a good yield and 6, to an azine (9) even upon standing at room temperature. 2 was treated with benzoic acid in ether to give 5-nitro-2-furfuryl benzoate (10) in a quantitative yield, and with triphenylphosphine in the same solvent to afford the triphenylphosphazine (13) in a 75% yield; this last substance liberated nitrogen very easily in the presence of cuprous ions to give the phosphonium ylid (14), one of the Wittig reagents. 14 was then considered as a possible starting material for preparing (5-nitro-2-furyl)ethylenic compounds. Similarly, 3-(5-nitro-2-furyl)acrolein triphenylphosphazine (17) was prepared from 4 and triphenylphosphine.