Structure of an unsymmetrical isomer from the attempted synthesis of 1,8-dicyclooctatetraenylnaphthalene.

Abstract

Attempted synthesis of 1,8-dicyclooctatetraenylnaphthalene (1) by the palladium(0)-catalyzed coupling of 1,8-dibromonaphthalene with cyclooctatetraenyltrimethylstannane afforded a single unsymmetrical isomer of 1 in 88% yield. Two-dimensional NMR methods and spectral synthesis were employed to assign the structure of the isomer (2). AM1 geometry-optimized structures of 2 and its isomers showed that the unexpected unsymmetrical structure of 2 results from the minimization of repulsive inter-ring H-H interactions. Compound 2 is postulated to arise via tandem [2 + 2] cycloaddition and 6 pi --> 4 pi + 2 sigma electrocyclization reactions of 1.