Naphtho[1,2-b]thiophen. Part I. Preparation and electrophilic substitution
Naphtho[1,2-b]thiophen was prepared from 3,4-dihydronaphthalen-1 (2H)-one by a five-stage process. Bromination, formylation, acetylation, and lithiation of naphtho[1,2-b] thiophen occurred at the 2-position. Nitration gave a mixture of the 2- and 5-nitro-derivatives; the structure of the latter was confirmed by transforming it into the 5-bromo-compound, which could be prepared unambiguously. Bromination and nitration of ethyl naphtho[1,2-b]thiophen-2-carboxylate gave mainly the 5-substituted compound in each case.