Unusually direct synthesis of mono- and di-substituted tetrathiafulvalenes

Direct reaction of norbornadiene, tributylphosphine, carbon disulfide and acetylenic diesters affords the norbornene-fused dihydrotetrathiafulvalenes 7 in addition to the bis-adducts 4 and for less reactive acetylenic dipolarophiles only 7 is isolated. Upon flash vacuum pyrolysis the compounds 7 undergo a retro Diels-Alder reaction to give substituted tetrathiafulvalenes 8. By using the norbornadiene diester in place of norbornadiene with DMAD, 8a can be obtained in higher overall yield. Attempted isolation of the zwitterionic structure 9 instead gave a rearrangement product with the novel 1,2,5-trithiepane stabilised ylide structure 11. (C) 1999 Elsevier Science Ltd. All rights reserved.