Studies on the Dimerization of 2-Benzylidene-1-indanone

It has been observed that 2-(E)-benzylidene-1-indanone (1) undergoes dimerization under basic conditions. The reaction is highly stereoselective and provides almost exclusively dimer 2b using NaHCO(3)/DMF, guanidine carbonate/DMF, or Cs(2)CO(3)/CH(3)CN. The structure and the relative stereochemistry of compound 2b were initially established on the basis of COSY, HMQC, HMBC, and NOESY NMR correlation techniques. The structure and the stereochemistry were then confirmed by X-ray crystallographic analysis. Two other stereoisomers were obtained, in minor proportions, by varying the experimental conditions. A fourth isomer was also produced using 2-(Z)-benzylidene-1-indanone as the starting material.