1,2,5-TRITHIEPIN - A 10-PI-ELECTRON HETEROAROMATIC SYSTEM

The unsubstituted 1,2,5-trithiepin (1) has been synthesized from the k nown 1,2,5-trithiepane (6) through two consecutive Pummerer rearrangem ents. Proton and carbon NMR spectra were completely analyzed, assigned , and correlated. The protons in 1 are shifted downfield by Delta delt a = 0.57 ppm for H-3/H-7 (delta = 6.57 ppm) and by 1.10 ppm far 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 characterizi ng 1,2,5-trithiepin (1) as the first multisulfur 10 pi-aromatic diatro pic molecule incorporating a disulfide linkage. 6,7-Dihydro-1,2,5-trit hiepin (7) is a dynamic system. Variable-temperature H-1-NMR measureme nts of 7 yielded an estimated free energy of activation at the coalesc ence temperature (227 K) of Delta G(double dagger) = 9.83 kcal/mol.