Diels -Alder reactions of [60]fullerene with 1,2,4,5-tetrazines and additions to [60]fullerene-tetrazine monoadducts
The Diels-Alder reaction between [60]fullerene and 1,2,4,5-tetrazines was studied. Under conditions of total darkness, [60]fullerene reacts with tetrazines to form bicyclic intermediates which immediately extrudes nitrogen to yield C2nu symmetric monoadducts. Thus, 3,6-diphenyl and 3,6-di-(2 '-pyridyl)-1,2,4,5-tetrazines react with [60]fullerene to form the corresponding C2nu symmetric monoadduct. To successfully synthesize these [60]fullerene-tetrazine monoadducts, the Diels-Alder reactions must be run in total darkness. In the presence of light and acid catalyst, the monoadducts are susceptible to nucleophilic attack by water leading to novel hydration/rearrangement products that contain 4,5-dihydropyrazole groups nested atop the [60]fullerene skeleton. The [60]-fullerene-tetrazine monoadducts also react with primary amines in a similar fashion. The proposed mechanism for the reaction between [60]fullerene-tetrazine monoadducts and primary amines is similar to that proposed for the hydration/rearrangement reaction. The [60]fullerene-tetrazine monoadducts also react with monoprotic nucleophiles such as thiols, alcohols, and secondary amines to yield racemic tetrahydropyridazine products. Nucleophilic attacks by nonanethiol, thiophenol, methanol and dimethylamine have all been studied and are all are proposed to proceed along a similar pathway.
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