1,2,5-Trithiepin: A 10pi-Electron Heteroaromatic System.
The unsubstituted 1,2,5-trithiepin (1) has been synthesized from the known 1,2,5-trithiepane (6) through two consecutive Pummerer rearrangements. Proton and carbon NMR spectra were completely analyzed, assigned, and correlated. The protons in 1 are shifted downfield by Deltadelta = 0.57 ppm for H(3)/H(7) (delta = 6.57 ppm) and by 1.10 ppm for H(4)/H(6) (delta = 7.24 ppm) relative to the 6,7-dihydro-1,2,5-trithiepin (7). These downfield shifts are comparable to thiophene, thus characterizing 1,2,5-trithiepin (1) as the first multisulfur 10pi-aromatic diatropic molecule incorporating a disulfide linkage. 6,7-Dihydro-1,2,5-trithiepin (7) is a dynamic system. Variable-temperature (1)H-NMR measurements of 7 yielded an estimated free energy of activation at the coalescence temperature (227 K) of DeltaG() = 9.83 kcal/mol.
Ueng
Shou-Nan
SN
Department of Chemistry, Hunter College, CUNY Graduate Center, 695 Park Avenue, New York, New York 10021.
Blumenstein
Michael
M
Grohmann
Klaus G.
KG