Abstract
While exhibiting a nitrogen basicity comparable to that of aniline, 3,4-diaminothiophene (DAT) does not show any tendency to react as a nitrogen nucleophile with a highly electrophilic compound like 4,6-dinitrobenzofuroxan (DNBF). Depending upon the experimental conditions employed, the addition of DNBF takes place at C-2 to give a carbon-bonded monoadduct (3,H) or at C-2 and C-5 to give a C,C-diadduct (4,H) which exists as a mixture of two diasteromers. Both the acid and base forms of these adducts have been characterized. A kinetic study of the monocomplexation of DAT and its 2,5-dideuteriated analog have been carried out at various pH in 50% H 2 O-50% Me 2 SO. The results shows that electrophilic attack by DNBF is the rate-limiting step of the formation of the adduct 3,H. The measured rate constant for DNBF addition is very high emphasizing the very strong nucleophilic character of the C α positions of DAT and supporting the idea that this compound is strongly enaminic in nature
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