Substitution reactions of naphtho[2,1-b]thiophen. Part II. Influence of substituents in the thiophen ring

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Abstract
The nuclear bromination, formylation, Friedel–Crafts acylation, and metalation reactions of 1-methylnaphtho-[2,1-b]thiophen occur in the 2-position. Nitration gives a mixture (9 : 1) of the 2- and the 5-nitro-derivatives. The identity of the 5-nitro-derivative is confirmed by its conversion into the corresponding 5-bromo-compound, which is compared with an authentic sample. Nuclear bromination and nitration of 2-methylnaphtho[2,1-b]-thiophen, and the bromination of 1,2-dimethylnaphtho[2,1-b]thiophen and 1-formyl- and 2-formyl-naphtho-[2,1-b]thiophen occur in the 5-position. It is suggested that the lack of reactivity of the 1-position in naphtho-[2,1-b]thiophen and its derivatives may be due to steric interaction with the nearby 9-position.

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