Indeno-polycyclic aromatic hydrocarbons: A versatile new synthetic route

Acylation of a polycyclic aromatic hydrocarbon (PAH) adjacent to a ring jun ction with 2-bromobenzoyl chloride followed by Flash Vacuum Pyrolysis (FVP) of the resulting bromoketone affords the corresponding indeno-annulated PA H. The new method is illustrated by syntheses of indeno[1,2,3-cd]pyrene (1) from pyrene and indeno[1,2,3-cd]fluoranthene (2) from fluoranthene. The fo rmation of indeno[1,2,3,4-defg]chrysene (11) from FVP of 8-(2-bromobenzoyl) fluoranthene (10), and as a secondary product from FVP of 3-(2-bromobenzoyl )fluoranthene (9), reveals the ability of phenyl groups to migrate around t he periphery of a didehydro-PAH. Mechanisms involving reversible hydrogen a tom transfers are proposed. Diacylation of fluoranthene with 2-bromobenzoyl chloride followed by FVP gives the previously unknown, nonplanar, nonalter nant, C28H14 PAH diindeno[1,2,3,4-defg:1,2,3-rs]chrysene (21) in just two s teps.