SYNTHESIS, CHARACTERIZATION, AND MOLECULAR-STRUCTURE OF [6](9,10)ANTHRACENOPHANE AND ITS PERI-SUBSTITUTED DERIVATIVES - THE SMALLEST 9,10-BRIDGED ANTHRACENES

[6](9,10)Anthracenophane (1a) was synthesized by the benzoannelation m ethod starting from dibromo[6]paracyclophane 6 via diepoxyanthracenoph anes 3a and 4a. In a similar fashion, peri-substituted derivatives, te tramethyl (1b) and tetraphenyl (1c), were synthesized through the corr esponding diepoxyanthracenes 3b, 4b, and 3c. Molecular structures of t etramethyldiepoxyanthracenophanes 3b and 5b are discussed with regard to the Mills-Nixon effect on the basis of their X-ray structure analys es. The parent anthracenophane 1a is extremely air- and acid-sensitive , so it is characterized spectroscopically as a mixture containing its dihydro derivative 8a. The peri-substituted derivatives 1b and 1c are more stable than 1a, and are fully characterized by spectroscopic met hods and X-ray crystallographic analyses. X-ray structures reveal that the out-of-plane deformation angles of the bridged aromatic ring of 1 b and 1c are the largest observed in any short-bridged [n]cyclophanes. Semiempirical AM1 calculations indicate that the out-of-plane deforma tion of the aromatic rings 1b and 1c is more severe than that of 1a du e to the steric repulsion between the benzylic methylenes and the peri substituents. That the kinetic stability observed for 1b and 1c was g reater than that of 1a is, therefore, ascribable to the steric protect ion of the reactive bridgehead carbons by the peri substituents. Acid- catalyzed rearrangement of 1a-c gave the corresponding methylenedihydr o isomers 2a-c, which represent the first examples of bridged methylen edihydroanthracenes. Photochemical isomerization of 1b and 1c took pla ce readily, giving the corresponding Dewar anthracenes 11b and 11c. Th ermal cycloreversion of 11b and 11c gave the cyclophanes 1b and 1c wit h E(a) values of 22.3 and 25.4 kcal/mol, respectively.