Dibenzothiepins, phthalans and phthalides from 4-heterosubstituted dibenzothiins

The lithiation of 4-heterosubstituted dibenzothiins (phenoxathiin, phenothiazine and thianthrene) with lithium and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 7.5% molar) in THF at temperatures ranging from −90 to −78°C gives the corresponding functionalised organolithium intermediate , which by reaction with different electrophiles [H2O, D2O, ButCHO, PhCHO, Ph(CH2)2CHO, Me2CO, Et2CO, (CH2)5CO, (CH2)7CO] at the same temperature, followed by hydrolysis, gives the expected functionalised thiols . Cyclisation of some thiols under acidic conditions leads to the corresponding seven-membered dibenzo heterocycles . In the case of thianthrene , after addition of a carbonyl compound as the first electrophile [MeCHO, ButCHO, Me2CO, Et2CO, (CH2)5CO], the corresponding intermediate can be lithiated again and react with a second electrophile. Diols are obtained after hydrolysis when a carbonyl compound [ButCHO, PhCHO, Ph(CH2)2CHO, Me2CO, Et2CO, (CH2)5CO] is used as the second electrophile. Acidic cyclisation of diols gives substituted phthalans in almost quantitative yields. Finally, in the case of using carbon dioxide as the second electrophile, phthalides are obtained after acidic hydrolysis.