Thianthrene as a source of the 1,2-benzene dianion

The lithiation of thianthrene 1 with lithium and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 4% molar) in THF at −90°C, followed by reaction with a carbonyl compound [ButCHO, Me2CO, Et2CO, (CH2)5CO] at the same temperature, gives an intermediate, which was lithitated again and reacted with a second carbonyl compound [ButCHO, PhCHO, Ph(CH2)2CHO, Me2CO, Et2CO, (CH2)5CO] to give, after the final hydrolysis, the expected diols 2. Compounds 2 are easily cyclised under acidic conditions (85% H3PO4) to yield the expected phthalans in almost quantitative yields. Finally, when after the reaction with the first carbonyl compound (PhCHO, Me2CO), carbon dioxide was used as the second electrophile, the expected substituted phthalides 3 were obtained after acidic work-up.