The first step in the second method was an alkoxide catalysed condensation of dlethylsuccinate and 9-fluorenone (a Stobbe reaction). An intensive study was made of this reaction, so that the structure of Its various products could be firmly established. These were found to be the mono-condensation products, 3:3'-diphenylene-2-carbethoxyvinylacetic acid and the dibasic acid, 3:3'-diphenylene-2-carboxyvinylacetic acid whose structures were established by esterification, hydrolysis, reduction and bromination experiments, and the dicondensation product 1:4- bisdiphenylene-2:3-decarboxybutadlene whose structure was elucidated by decarboxylation to the known hydro-carbon. Reduction of the lactone produced by the decarboxylation of the mono-condensation products gave the 9-fluorenyl-2-propionic acid.

The first of these methods resulted from investigations of the trimethylbenzylammonium hydroxide catalysed condensation of acrylonitrile with 9-substitutad fluorenes, the initial condensation in the preparation of the above acid being with 9-fluorenol. Acrylonitrile was also condensed with 9-phenylfluorene, and the product hydrolysed to an acid cycllsable to a ketone, but acrylonitrile could not be condensed with 9-chloro-, 9-ethyl, and 9-benzylfluorenes, nor with 1-keto-l'(9'-fluorenyl) acetic acid.

It was also found that the 9-fluorenyl-2- propionic acid, and the substituted 9-fluorenyl-2- propionic acids prepared, were very resistant to cyclisation, the only method from which crystallisable products were obtained being acid chlorideFrledel-Crafts methods.

It was found that fluorene condensed with molecular amounts of cinnamnitrile (phenylacrylonitrile) under the catalytic action of trimethylbenzylammonium hydroxide and the product hydrolysed to an acid cyclisable to a ketone.

Two new methods have been evolved for the preparation In improved yields of 9-fluorenyl-2- proplonic acid, from which fluoranthene has been synthesised, thus confirming the work of von Braun.