The synthesis of some fluoranthene derivatives from acenaphthene

Abstract

The polycyclic aromatic hydrocarbon, dibenzo[ghi,mno]fluoranthene (I), has recently been synthesised. This compound will most probably be considerably strained because of the appreciable deviation of the bond angles from the normal value found in benzenoid compounds. Barth and Lawton Barth and Lawton, J.A.C.S., 88, 380 (1960). who prepared (I) have considered the possibility of contribution by a polar resonance form such as (II) to the actual electronic distribution of the system. A molecular orbital calculation has indicated that the polar form would probably contribute to the molecule and that the structure has considerable resonance energy. The polar resonance form has a unique structure in that it is composed of two charged concentric conjugated systems; the outer being a cyclopentadecahepteryl cation and the inner a cyclopentadienyl anion. Both of these annular conjugated systems satisfy the requirements of Huckel's 4n+2 rule. Barth and Lawton have assigned a trivial name, corannulene, to the compound dibenzo[ghi,mno]fluoranthene. This name is derived from the Latin cor meaning heart and annula meaning ring. Their twelve-step synthetic route from methyl-4,5methylenephenanthrene-3-carboxylate is shown on page 3. The objective of this work was the synthesis of the corannulene ring system by a completely different pathway, using acenaphthene as the starting material. The proposed methods of preparation involve the formation of a number of fluoranthene derivatives substituted in the 7- and 10-positions. As very few of these compounds have been reported additional interest would derive from the synthesis of the corannulene ring system.