Benzo[b]fluorenes formed in the thermal cyclization of 3-ene-1,6-diynes

摘要

A three-step preparation of the benzofluorene core is presented. The last step involves thermal cyclization of 3-ene-1,6-diyne (7) leading to the formation of four benzofluorene derivatives, one of which has been investigated by X-ray analysis. The harsh thermal conditions indicate that the cyclization of 7 might not proceed via a biradical intermediate as would be anticipated by a mechanistic proposal from Ueda. [References: 21]