Cyclobutarenes. Part 1. Synthesis of cyclobutanaphthalene and phenanthrene derivatives

Preparations of 1,2-bis(dibromomethyl)naphthalene (7) and 9,10-bis(dibromomethyl)phenanthrene (8) are described; reaction of these compounds with sodium iodide at 60 °C gives 1,2-dibromo-1,2-dihydrocyclobuta[a]naphthalene (3) and 1,2-dibromo-1,2-dihydrocyclobuta[/]phenanthrene (4). 2,3-Bis(dibromomethyl)naphthalene (5) cyclises at 120 °C to give 1,2-dibromo-1,2-dihydrocyclo-buta[b]naphthalene (2) and 6,13-dihydro-6,13-ethenopentacene (10).