106 Furans and Thiophenes
A route to thiophenes, which certainly mirrors the biosynthesis of naturally occurring thiophenes, is the very simple
and effective reaction between a 1,3-diyne and sulfi de or hydrogen sulfi de. The diyne is, of course, at the same oxida-
tion level as a 1,4-diketone; the fi rst step may be direct formation of a thioenolate by nucleophilic addition of hydrogen
sulfi de to one of the alkynes.
Exercises
- What would be the structures of the products of carrying out Vilsmeier reactions with 2-methyl- and
3-methylthiophenes? - Suggest structures for the major and minor isomeric products, C 5 H 5 NO 3 S, from 2-methoxythiophene with
HNO 3 –AcOH at 20 °C. - What would be the principal site of deprotonation on treatment of 2- and 3-methoxythiophenes with
n-BuLi? - How could one prepare n-decane from thiophene?
- Write structures for the products of reaction of:
(i) furfuryl alcohol with H 2 C=C=CHCN→ C 9 H 9 NO 2 ; and
(ii) 2,5-dimethylfuran with CH 2 =CHCOMe/15 kbar. - How could one prepare:
(i) 2,5-diethylthiophene; and
(ii) 2,5-diphenylfuran? - What is the structure of the thiophene C 11 H 16 S obtained from 3-acetylcyclononanone with P 4 S 10?
- For the synthesis of tetronic acid summarised as follows, suggest structures for the intermediates: methyl-
amine was added to dimethyl acetylenedicarboxylate (DMAD) → C 7 H 11 NO 4. Selective reduction of one of
the esters in this product with LiAlH 4 then gave C 6 H 11 NO 3 , which, with acid, cyclised → C 5 H 7 NO 2 , aqueous
acidic hydrolysis of which produced tetronic acid.