A convenient procedure for the synthesis of tetrathia--helicene and the selective alpha-functionalisation of terminal thiophene ring
Maiorana, S × Papagni, A Licandro, E Annunziata, R Paravidino, P Perdicchia, D Giannini, C Bencini, M Clays, Koen Persoons, Andre #
Pergamon-elsevier science ltd
Tetrahedron vol:59 issue:34 pages:6481-6488
This paper describes a convenient preparation of tetrathia--helicene (TH), the generation of the alpha-anion on the terminal thiophene ring, and the synthesis of the 2-formyl-tetrathia--helicene (2-CHO-TH). The key intermediate trans-1,2-dibenzodithiopheneethene, prepared in 97% yield by McMurry coupling of the 2-formyl-benzo[1,2-b;4,3-b']dithiophene, was transformed into TH using a known procedure. The described method affords TH in 46% overall yield, which is more than four times the yield previously reported in the literature. The alpha-anion of TH, which is easily generated on the alpha-position of one of the terminal thiophene rings, reacts with electrophilic reagents such as D2O and DMF. The latter reaction proved to be the best way to prepare 2-CHO-TH, a key intermediate for the preparation of new substituted heterohelicenes. (C) 2003 Elsevier Ltd. All rights reserved.