SYNTHESIS AND STEREOCHEMISTRY OF ORTHO-METHYLATED OCTAPHENYLNAPHTHALENES

Two exceptionally crowded derivatives of octaphenylnaphthalene bearing ortho-methyls on the phenyl ubstituents-2,3,5,6,7,8-hexaphenyl-1,4-di (o-tolyl) naphthalene (2) and 2,3,6,7-tetraphenyl-1,4,5,8-tetra (o-tol yl) naphthalene (3)-were prepared by the addition of tetraarylbenzynes to tetraarylcyclopentadienones. Both compounds exist as a mixture of conformational isomers which do not interconvert at ordinary temperatu res. The yield of 2 and its distribution of conformers is strongly inf luenced by the choice of precursors in the final cycloaddition; one me thod gives a high yield of a 55:45 trans-2:cis-2 mixture, while anothe r gives a very low yield of a 15:85 trans-2:cis-2 mixture. Kinetic epi merization of the latter indicated that the barrier to rotation about the tolyl-naphthalene bonds is 33.1 kcal/mol. (C) 1998 Wiley-Liss, Inc .