title: Evidence of Transannular Bonding Interaction between Two Sulfur Atoms on Photolysis of Naphtho[1,8-ef][1,4]dithiepins.
abstract: Naphtho[1,8-ef][1,4]dithiepins 5 were prepared by the reaction of naphtho[1,8-de]-1,3-dithiins 3 with diethyl diazomalonate in the presence of copper acetylacetonate. The X-ray crystallographic analysis of 2,3-dihydro-2,2-bis(ethoxycarbonyl)-3-phenylnaphtho[1,8-ef][1,4]dithiepin (5a) revealed that the S.S distance is shorter than the sum of their van der Waals radii, indicating that compounds 5 have a strong through-space interaction between the two sulfur atoms. Direct irradiation of 5 with a 500 W high-pressure mercury lamp (313 nm) at room temperature gave the corresponding olefins 6 and naphtho[1,8-cd]-1,2-dithiole (1) quantitatively. The quantum yields of the consumption of 5a and the formation of 6aand 1 were 0.34. The mechanism of this reaction was investigated by examining the effect of sensitization and light intensity. The results indicate that the reaction may proceed by a one-photon process from an excited singlet state. Ab initio calculations were carried out on model compound 7, and it was shown that the excitation to the S(1) state causes a bonding interaction between the two sulfur atoms, making the reaction possible.
authors.affiliation: Tsukuba Advanced Research Alliance Center, Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki 305, Japan.
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Fujii
authors.forename: Ohgi
authors.initials: O
authors.lastname: Takahashi
authors.forename: Naomichi
authors.initials: N
authors.lastname: Furukawa