1. H. D. Hartough and S. L. Meisel, Compounds with Condensed Thiophene Rings, Interscience. New york (1954).
2. 1. L. Gatterrmann and A. Lockhart, On thionaphthene, Chem. Ber. 26, 2808-2809 (1893)
3. 2. A. Boes. Centralblatt II 804 (1902).
4. F. Challenger and J.B. Harrison, Sulphur compounds of technical interest. The isomeric thiophthens. J. Inst. Pet. Tech. 21. 135–154 (1935).
5. P. Cagniant and D. Cagniant, Recent advances in the chemistry of benzo[b]furan and its derivatives. Adv. Heterocyclic Chem. 18. 337–482 (1975); A. Mustafa, Benzo(b)furans. Chemistry of Heterocyclic Compounds, Vol. 29, Wiley-Interscience, New York (1974).