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A convenient procedure for the synthesis of tetrathia-[7]-helicene and the selective α-functionalisation of terminal thiophene ring

✍ Scribed by Stefano Maiorana; Antonio Papagni; Emanuela Licandro; Rita Annunziata; Piero Paravidino; Dario Perdicchia; Clelia Giannini; Marco Bencini; Koen Clays; André Persoons

Book ID
104205626
Publisher
Elsevier Science
Year
2003
Tongue
French
Weight
209 KB
Volume
59
Category
Article
ISSN
0040-4020

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✦ Synopsis

This paper describes a convenient preparation of tetrathia-[7]-helicene (TH[7]), the generation of the a-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 0 ]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 a-anion of TH [7], which is easily generated on the a-position of one of the terminal thiophene rings, reacts with electrophilic reagents such as D 2 O 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.

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