Synthesis and photoreactions of some spiro[cycloalkanephenalenes]

Reaction of the phenalenyl anion (1⁻) with 1,2‐dibromoethane, 1,4‐dibromobutane and 1,5‐dibromopentane results in the formation of (bromoalkyl)phenalene derivatives. These derivatives undergo ring closure when treated with base to spiro[cyclopropane‐1,1′‐[1H]phenalene] (2), spiro[cyclopentane‐1,1′‐[1H]phenalene] (4) and spiro[cyclohexane‐1,1′‐[1H]phenalene] (5). Reaction of 1⁻ with 1,3‐dibromopropane gives a 1:1 mixture of 1,2,3,5‐tetrahydropyrene (3a) and 1,2,3,6‐tetrahydropyrene (3b), both of which can easily be dehydrogenated to pyrene. Photochemical reactions of spiro[cycloalkanephenalenes] 2, 4 and 5 are discussed. The introduction and photochemical opening of a spirocyclopropane ring in phenalene results in the formation of 1,2‐dihydro‐4H‐cyclopenta[cd]phenalene (6), a compound with a fused five‐membered ring. The construction of pyrene and cyclopenta[cd]phenalene skeletons starting from phenalene represents a new approach in the synthesis of polycyclic aromatic hydrocarbons and their derivatives.