4-Nitrobenzodifuroxan: a highly reactive nitroolefin in Diels–Alder reactions

The reactions of 4-nitrobenzodifuroxan (NBDF) with a series of common dienes are found to proceed very readily to afford stable cycloadducts, which are the result of highly stereoselective normal electron demand (NED) Diels–Alder reactions. Due to the additional activation provided by the two adjacent furoxan rings, the nitroolefinic double bond of NBDF is also prone to undergo NED reactions with less reactive dienic structures such as the enol form of ethoxymethyleneacetylacetone and the in situ generated 2-ethoxy-4-(2-furfuryl)buta-1,3-diene. A number of X-ray structures could be obtained, which leave no doubt as to the stereochemistry of the resulting cycloadducts. A rationalization of the reactions in terms of the electrophilicity parameter ω defined by Parr suggests that all cycloadditions proceed with a notable polar character.