The synthesis of some o-terphenyls and fluorenones

Abstract

Heptahelicene Flammang-Barbieux, Tet. Letters, 8, 743 (1967). (1), octahelicene (2) and nonahelicene Martin, Tet. Letters, 3507-10 (1968). have been synthesised photochemically, and all belong to an interesting class of purely aromatic hydrocarbons which owe their asymmetry to a helical shape resulting from a forced overlap of rings due to intramolecular overcrowding; they can therefore be left- or right-handed in orientation and hence should be optically active Martin, Tet. Letters, 3507-10 (1968). Another very interesting helical and hence optically active compound is trans-cyclooctene (4), in which the carbon-chain must lie above the plane of the double bond on one side and below it on the other Cope, Ganellin, Johnson, Jr., Van Auken and Winkler, J.A.C.S. 85 3276 (1963)., Cope, Banholzer, Keller, Pawson, Whang and Winkler, J.A.C.S. 87 3644 (1965). The yet unknown parent system, indeno[2,1-C]phenanthrene, (24), would also be expected to exhibit similar asymmetry due to its intra-molecular overcrowding between the end rings, marked with asterisks. The object of this work is to investigate possible syntheses of compounds obtainable from the intermediate 3'-carboxy-6'-methyl-o-terphenyl, (12), with an aim of ultimately synthesising the parent compound (24). Starting from (12), a number of new angular polycyclic aromatic hydrocarbons could be made, apart from compound (24), such as the following: