A new simple and efficient way to 3-hydroxy(methoxy)thiophenes is described. The reactions
of (ethylsulfanyl)acetyl fluoride/boron trifluoride (1) and 2-(ethylsulfanyl)butanoyl fluoride/boron trifluoride (6) complexes with acetylenes give rise to the 5-membered cyclic sulfonium salts (3a-f). The last ones (3e, 3f) after being refluxed with thiourea in methanol or acetonitrile are converted into
3-methoxythiophenes or 3-(2H)-thiophenones respectively. Several 3-methoxythiophenes unsubstituted in the 2-position
were obtained by the reactions of 1 with acetylenes. Reactions of 6 with acetylenes allows the synthesis of 2-ethylsubsituted 3-methoxythiophenes. The
method allows the synthesis of a variety of mono-, di-, tri- and tetrasubsituted thiophenes.
acylation - thiophene - acylsulfonium salt - alkynes - electrophilic addition
