Synthesis of some highly functionalized thiophene-3-carboxylates and alcohols

Article abstract of DOI:10.1002/jhet.5570330328

Highly functionalized thiophenes are prepared by two methods. The first uses a lithium-halogen exchange reaction on a trisubstituted 5-bromothiophene 25 to generate the corresponding 5-lithiothiophene 26 which is then reacted with either dimethylformainide or formaldehyde to give the 5-formyl 28 or 5-hydroxymethylthiophene derivative 31 in good yields. These are further transformed to other tetrasubstituted thiophenes. The second method assembles the thiophene ring from three components: a benzyl mercaptan, an aldehyde, and a vinylphosphonate 10. Thus, the benzyl mercaptan is dilithiated then reacted with an appropriate aldehyde to afford a 2-mercapto-2-phenylethanol derivative 37. Michael addition of 37 to 10 followed by oxidation of the hydroxyl group furnishes ketophosphonate 39. An intramolecular Wittig-type reaction produces the thiophene skeleton.