Dibenzo-dithiepine

The central ring of both dibenzo[l,4]- dithiins and -oxathiins is cleaved on treatment with Li and a catalytic amount of 4,4"-di-rert-butylbiphenyl (DTBB) to afford thiols after reaction of the dilithio intermediate with electrophiles. In certain instances, the initial product can be cyclised to the dibenzo- dithiepine and -oxathiepine <02CL726>. The dilithio salt from thianthrene reacts sequentially with two different carbonyl compounds to give a l,2-di(hydroxyalkyl)benzene. When C02 is used as the second electrophile, a phthalan results <02TL7205>. 

The aromatic character of the dibenzo derivative 2 has also been calculated. Studies on the behavior of the deep red anion 3, as a potential IOji heteroaromatic system, were described previously <1996CHEC-II(9)268>. H NMR spectra (NMR - nuclear magnetic resonance) of l,3-dithiepin-2-carbodithiolate 4, a ligand obtained from the reaction of carbon disulfide with the lithium salt of 1,3-dithiepin, as well as its palladium salt suggest a good deal of Hiickel aromatic character in the seven-membered dithiepin ring <1991ICA(185)169>. 

Dibenzo-fused dithiepins undergo photochemically induced ring contractions. Thus, irradiation of 2-phenyldibenzo-[df [l,3]dithiepin 1-oxide 72 <1999T5027> and 9-phenyl-4,8,9-trithiadibenzo[i2/,9]azulene 8-oxide 70 <1996CL655> using a high-pressure mercury lamp (400 W) gave disulfides 99 and 100 (Scheme 22). 

The preparation of dibenzo-fused dithiepins was usually catalyzed by BF3 Et20. For example, the synthesis of dibenzo[7//][l,3]dithiepin from 1,1 -binaphthalene-2,2 -dithiol and dibromomethane and diiodomethane, respectively, failed however, reaction of the dithiol with dimethoxymethane in the presence of BF3-Et20 afforded the desired dithiepin in 71% yield <1995T787>. 

---