1,2,5‐Oxadiazole (Furazan) Derivatives from Benzoylnitromethane and Dipolarophiles in the Presence of DABCO: Structure and Intermediates

Abstract

Furazan (1,2,5‐oxadiazole) derivatives are obtained along with isoxazolines from the reaction of benzoylnitromethane with dipolarophiles in the presence of DABCO. Furazans are shown to derive from the intermediate dibenzoylfuroxan (3,4‐dibenzoyl‐1,2,5‐oxadiazole‐5‐oxide) and dipolarophiles under hydrolytic conditions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

1,4‐Diazabicyclo[2.2.2]octane (DABCO) as an Efficient Reagent for the Synthesis of Isoxazole Derivatives from Primary Nitro Compounds and Dipolarophiles: The Role of the Base

“…These side products have been identified as furazan derivatives, which are produced from the dibenzoylfuroxan intermediate. [24] Similarly, the reaction of 1a with the same dipolarophiles afforded some diacetylfuroxan as a side product, in addition to the expected cycloadducts.…”

“…A considerable amount of furazan is produced with these tertiary amines, via the dibenzoylfuroxan intermediate. [24] Nitroacetone (1a) behaves similarly; diacetylfuroxan is found as a byproduct (see above).…”

“…However, in the reactions with DABCO, the identification of 3,4-diacetylfuroxan among the reaction products of nitroacetone (1a) and the identification of furazans derived from 3,4-dibenzoylfuroxan among the reaction products of benzoylnitromethane (1b) [24] suggests that in these cases (at least in part) the nitro compound undergoes dehydration prior to cycloaddition. However, nitroacetone (1a) and benzoylnitromethane (1b) react faster in the presence of the dipolarophile than in its absence, and the cycloadducts are the main products even with no excess of dipolarophile.…”

“…Analytical and spectroscopic data were identical to those previously reported. [24] Isoxazolidine 6b: Light yellow oil. Yield 106 mg, 100 %.…”

Synthesis of 3,5-Disubstituted Isoxazoles and Isoxazolines in Deep Eutectic Solvents

“…The second one is the 1,3-dipolar cycloaddition reaction between alkynes or alkenes with nitrile oxides, generated in situ from aldoximes or nitroalkanes. [12][13][14][15][16][17][18][19][20][21][22][23] In turn, these heterocycles can be transformed into β-functionalizes carbonylic compounds, 24 by cleavage of the labile N-O heterocyclic bond.…”