Chemistry Letters, Vol.29, No.5, 498-499, 2000
Z/E selectivity on the formation of 2,2'-diacyl-9,9'-bifluorenylidenes was controlled by the length of acyl side chains
Reaction of 2-acetyl-9-bromofluorene with base afforded Z- and E-2,2'-diacetyl-9,9'-bifluorenylidene in a ratio of 30/70. A similar treatment of 2-stearoyl-9-bromofluorene gave the corresponding bifluorenylidene in a Z/E ratio of 90/10. The observed dependency of Z/E ratio on the chain length is attributable not to steric repulsion, but to intra- and/or inter-molecular attractive forces between the side chains.