The vast majority of nucleophiles used so far were nitrogen, oxygen and sulfur nucleophiles as well as carbanions derived from acidic methylene compounds. Reactions between organometallic reagents and 1,2-dithioIium salts 1 have hardly been investigated. Liittringhaus and PrinzbachL21 obtained the 2,3-dithiafulvalenes 2 from sodium tetraphenylcyclopentadienide and 3-methylthio-l,2-dithiolium methosulfates, whereas Gompper and Guggenbergerc31 isolated the 2.3-dithiafulvalene 3 from the reaction of sodium pentakis(methy1thio)cyclopentadienide with 3-methylthio-5-phenyl-1,2-dithiolium perchlorate. In both examples the cyclopentadiene ring is heavily substituted. We studied reactions of the 3,5-bis(methylthio)-I ,2-dithiolium salts l a -c (tetrafluor~borates [~] or iodides) with the alkali or thallium salts of unsubstituted cyclopentadiene or monoalkyl-substituted ~yclopentadiene[~1. Compound l a can be considered as a typical representative of 4-aryl-substituted, 1 c as a typical representative of 4-alkyl-substituted 3,5-bis(methylthio)-1,2-dithiolium salts. In general, complex mixtures of products were obtained; the main reaction pathway, however, starts with the cleavage of the S-S bond in 1 by the metal cyclopentadienide 4. The first ring-opened product is supposed to have structure 5 with the sulfur attached to C-5 of the cyclopentadiene. Such compounds tend to rearrange to the thermodynamically more stable 1-substituted cyclopentadienes 6 by a 1,5-H shift. In the presence of a base (e.g. alkali cyclopentadienides) an ionic deprotonation/reprotonation process might take place, which is quite rapid, even at -78°C [6]. In the absence of a base (e.g. thallium cyclopentadienides) a slower 1,5-sigmatropic hydrogen shift should give rise to the formation of 6 . The isolated products 7-10 are intramolecular Diels-Alder adducts; 7 and 8 are formed from the primary intermediate 5, whereas 9 and 10 are generated from the rearranged intermediate 6. Product 11/11' is the result of an intramolecular condensation reaction of anionic 5/6 with elimation of methanethiol. The 2,3-dithiafulvalene 12/12' originates from a nucleophilic attack of the metal cyclopentadienide 4 at C-3 of the 1,2-dithiolium salts 1.
Reactions with l aThe results of the ring-opening reactions of 1,3-bis(rnethy1thio)-1 ,Zdithiolium salts l a -c with the metal cyclopentadienides 4 are most readily understood by starting with