This paper describes a convenient preparation of tetrathia-[7]-helicene (TH[7]), the generation of the alpha-anion on the terminal thiophene ring, and the synthesis of the 2-formyl-tetrathia-[7]-helicene (2-CHO-TH[7]). 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[7] using a known procedure. The described method affords TH[7] in 46% overall yield, which is more than four times the yield previously reported in the literature. The alpha-anion of TH[7], 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[7], a key intermediate for the preparation of new substituted heterohelicenes. (C) 2003 Elsevier Ltd. All rights reserved.
Maiorana, S., Papagni, A., Licandro, E., Annunziata, R., Paravidino, P., Perdicchia, D., et al. (2003). A convenient procedure for the synthesis of tetrathia-[7]-helicene and the selective α-functionalisation of terminal thiophene ring. TETRAHEDRON, 59(34), 6481-6488 [10.1016/S0040-4020(03)01056-1].
A convenient procedure for the synthesis of tetrathia-[7]-helicene and the selective α-functionalisation of terminal thiophene ring
PAPAGNI, ANTONIO;
2003
Abstract
This paper describes a convenient preparation of tetrathia-[7]-helicene (TH[7]), the generation of the alpha-anion on the terminal thiophene ring, and the synthesis of the 2-formyl-tetrathia-[7]-helicene (2-CHO-TH[7]). 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[7] using a known procedure. The described method affords TH[7] in 46% overall yield, which is more than four times the yield previously reported in the literature. The alpha-anion of TH[7], 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[7], a key intermediate for the preparation of new substituted heterohelicenes. (C) 2003 Elsevier Ltd. All rights reserved.
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