3-(4-Methoxy-2-methylbenzoyl)- and 3-(4-methoxy-2,5-dimethylbenzoyl)-benzo[b]thiophen underwent the Elbs reaction with rearrangment to give derivatives of benzo[b]naphtho[2,1-d]thiophen, whereas 2-(4-methoxy-2,5-dimethylbenzoyl)benzo[b]thiophen gave the normal cyclisation product, i.e. a benzo[b]naphtho[2,3-d]thiophen.