A cyclophane route to acenaphthyleno[1,2-e]pyrene. Relative bathochromic shifts (colour changes) in a series of 1,2-diaryl-acenaphthylenes

Abstract

1,2-Bis(3-methylphenyl)acenaphthylene 16 has been synthesized from acenaphthenequinone and 3-chlorotoluene. Bromination of 16 followed by an intramolecular cyclization with sodium sulfide affords the anti thiacyclophanene 18. Ring contraction reactions of 18 lead to the isolation of acenaphthylenopyrene 9 directly, presumably via valence isomerization of cyclophanediene 22 followed by oxidation of dihydropyrene 23. Photochemical desulfurization of 18 results in the isolation of the acenaphthylenodihydropyrene 28 via valence isomerization of cyclophanene 26 followed by oxidation of tetrahydropyrene 27. An increase in the degree of conjugation in going from 24 to 16 to 18 is evidenced by a visual colour change from orange to orange–red to red and a significant bathochromic shift in the electronic absorption in the range 400–450 nm. A bathochromic shift is also observed in going from 28 to 9, consistent with a more extended conjugated system in the latter. Complete assignment of the protons in 9 and 28 is achieved on the basis of ¹H COSY and NOESY spectra. There is no observable through-space scalar coupling between H-1 and H-14 in 9 but a strong NOE between them is evident. A tilting of the dihydropyrene moiety in 28 due to the stereochemical demand of its ethylene bridge results in an upfield shift of its H-1 and H-14 signals relative to those in 9.