ATTEMPTED SYNTHESIS OF BIS(ALKYLTHIO)-ORTHOQUINODIMETHANES FROM DITHIOBENZOATES

o-Alkyl substituted dithiobenzoates 3 are S-methylated with trimethylo xonium tetrafluoroborate to form the stable bis(alkylthio)arylmethyliu m tetrafluoroborates 4. Their deprotonation with LiHMDS takes place ei ther at the o-alkyl groups to form the postulated o-quinodimethanes 5 as intermediates or at the SMe groups to give the thiocarbonyl ylides 7. Both intermediates dimerize to furnish either the dibenzo[a,e]cyclo octenes 6 or the 1,4-dithianes 8/9. Their trapping with N-phenylmaleim ide (10) leads to the formation of the cycloadducts 11 or 12. The stru cture of 8e was confirmed by X-ray analysis. p-Substituted dithiobenzo ates 13 show a similar reaction sequence. Their bis(methylthio)arylmet hylium salts, however, are only deprotonated at one of the SMe groups to give the 1,4-dithianes 15/16. Sterically crowded 1,4-dithianes (e.g . 8d,e/9d,e) rearrange with traces of acid to the ring opened stilbene s 18 and 19.