Kinetics of the reactions of some 5-bromo-2-nitro-3-R-thiophens, 3,4-dibromo-2-nitro-5-R-thiophens, 3-bromo-2-nitro-5-R-thiophens, and 2-bromo-3-nitro-5-R-thiophens with nucleophiles in methanol

Abstract

The reactivity of some 5-bromo-2-nitro-3-R-thiophens (la–g; R = H, Me, Et, Prⁿ, n-hexyl, Pr¹, and Bu^t), 3,4-dibromo-2-nitro-5-R-thiophens (IIa and b; R = H and Me), 3-bromo-2-nitro-5-R-thiophens (IIIa and b; R = H and Me), and 2-bromo-3-nitro-5-R-thiophens (IVa and b; R = H and Me) with amines and sodium benzenethiolate has been studied in-methanol at various temperatures. Piperidinodebromination of compounds (la and c) has also been studied in benzene, in dioxan, and in dioxan-water (60 : 40 and 10 : 90). Independent of the position of the alkyl group (meta or para with respect to the leaving bromine), an unexpected alkyl activation has been observed, which represents a further exception to the electron-releasing behaviour of alkyl groups.