The lithiation of 4-heterosubstituted dibenzothiins I [phenoxathiin (X = O), phenothiazine (X = NMe) and thianthrene (X = S)] with lithium and a catalytic amount of 4,4'-di-tert-butylbiphenyl (DTBB) gives the corresponding functionalized organolithium intermediate, which by reaction with different electrophiles followed by hydrolysis, gives the expected functionalized thiols.Cyclization of thiols II (X = O; R1 = H, R2 = Ph; R1 = R2 = Et; X = S; R1 = H; R2 = tert-Bu, Ph) under acidic conditions leads to the corresponding seven-membered dibenzo heterocycles III.In the case of thianthrene (I; X = S), after addition of a carbonyl compound as the first electrophile, the corresponding intermediate can be lithiated again and be reacted with a second electrophile.Diols, e.g, IV, are obtained after hydrolysis when a carbonyl compound is used as the second electrophile.Acidic cyclization of diols gives substituted phthalans, e.g., V, in almost quant. yields.Finally, in the case of using carbon dioxide as the second electrophile, phthalides, e.g., VI, are obtained after acidic hydrolysis.
