SYNTHETIC AND SPECTROSCOPIC STUDIES OF POLYCYCLIC AROMATIC HYDROCARBONS: THE PREPARATION OF TRANS,TRANS-2,13;2',13'-DIETHENYLPENTAHELICENE, AN OVER AND UNDER FIGURE-EIGHT MOLECULE (STEREOCHEMISTRY, SULFONATION, PHOTOCHEMISTRY)
Abstract
The title compound, a chiral symmetric molecule, was prepared starting from 2,7-dimethylnaphthalene, with 2-methyl and 2,6-dimethylnaphthalene as models. Free radical bromination and reaction with triethylphosphite gave, after distillation, the monophosphite. Sommolet reaction of the bromide mixture gave the monoaldehyde, purified with sodium bisulfide. Low-valent titanium aldehyde coupling or Wadsworth-Emmons coupling gave trans-dinaphthyl-ethenes: unsubstituted, 6,6'-, 6,7' and 7,7'-dimethyl. Photochemical isomerization-ring closure on the unsubstituted and 7,7'-dimethylnaphthylethenes gave pentahelicene and 2,13-dimethylpentahelicene. Dibenzo{b,g}phenanthryl by-products were readily isolated. Final synthetic steps involved bromination of the dimethylpentahelicene, preparation of the bis-phosphonate (bromide plus triethylphosphite) and bis-aldehyde (bromide plus lithium 2-nitropropane anion) and coupling of bis-phosphonate and bis-aldehyde. Steric hindrance favors the formation of bis(bromomethyl)pentahelicene. Bis-phosphonate anion, generated at low temperatures with sodium hydride, reacted with bis-aldehyde to give the title compound and with two equivalents of 7-methyl-2-naphthaldehyde to give a dinaphthylethenyl model compound. Both were characterized by Proton NMR. An unsuccessful synthesis began with the sulfonation of 2-methylnaphthalene. NMR spectra of reaction mixtures and rediscovered thesis data clarified published results. At 95(DEGREES) 6-sulfonate is the major (40%) product with little or no 7-sulfonate. Short reaction time at 160(DEGREES) gives mainly 6-sulfonate, longer times a nearly equal mix of 6- and 7-isomers. The 7-sulfonate was isolated and characterized. Melting points for the sulfonyl chloride (80-82(DEGREES)) and sulfonamide (202-203(DEGREES)) differ from reported values. The barium salt of the 7-isomer is slightly more soluble than that of the 6-sulfonate. Extensive spectroscopic data (proton NMR, UV, MS) was analyzed for all compounds prepared. IR data shows longer wavelength hydrogen bending for 2,6-versus, 2,7-substituted naphthalenes. Proton NMR data was assigned for chemical shifts and coupling constants.
Degree
Ph.D.
Subject Area
Organic chemistry
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