Formation of 3-Sulfonyl-Substituted Benzo[a]heptalene-2,4-diols from Heptalene-1,2-dicarboxylates and Lithiomethyl Phenyl Sulfones

On treatment with 6 mol-equiv. of lithiomethyl phenyl sulfone at ?78° in THF, dimethyl 5,6,8,10-tetramethylheptalene-1,2-dicarboxylate ( 1′b ) gives, after raising the temperature to ?10° and addition of 6 mol-equiv. of BuLi, followed by further warming to ambient temperature, the corresponding 3-(phenylsulfonyl)benzoa]heptalene-2,4-diol 2b in yields up to 65% (cf. Scheme 6 and Table 2), in contrast to its double-bond-shifted (DBS) isomer 1b which gave 2b in a yield of only 6% 1]. The bisanion 9 ]^2? of the cyclopentaa]heptalen-1(1H)-one 9 (cf. Fig. 1), carrying a (phenylsulfonyl)methyl substituent at C(11b), seems to be a key intermediate on the reaction path to 2b , because 9 is transformed in high yield into 2b in the presence of 6 mol-equiv. of BuLi in the temperature range of ?10° to room temperature (cf. Scheme 7). Heptalene-dicarboxylate 1′b was also transformed into benzoa]heptalene-2,4-diols 2c – g by a number of lithiated methyl X-phenyl sulfones and BuLi (cf. Scheme 9 and Table 3).