9H-Fluorene-9-carbodithioic acids and dithioates. First isolation and characterization of a gem-enedithiol

[2,7-Bis(octyloxy)fluoren-9-yliden]methanedithiol (1a) and its tautomer 2,7-bis(octyloxy)-9H-fluorene-9-carbodithioic acid (2a) can be isolated in pure form from the reaction of monolithiated 2,7-bis(octyloxy)-9H-fluorene with CS₂ followed by protonolysis with aqueous HCl. Compound 1a is the first isolated and unambiguously characterized gem-enedithiol. When 9H-fluorene, 2,7-di-tert-butyl-9H-fluorene or 2,7-dimethoxy-9H-fluorene are used, the same synthetic procedure yields the unstable dithioic acids, which can be converted to the piperidinium salts.