The Tautomeric Structures of Some Alkylsubstituted 3-Hydroxythiophenes.

Chemical and spectroscopic properties of the 3-hydroxythiophene [thiophen-3(2H)-one] system

“…9 Previously, it was thought that, of the three possible monomethyl derivatives, only the 2-substituted compound 4 was stable enough for measurement of tautomeric equilibrium composition. 13 Our result for 4 (keto : enol 33 : 67 in chloroform) is in reasonable agreement with the published data (keto : enol 20 : 80, in CS 2 solution). The 5-methyl derivative 7 shows a much increased level of keto tautomer (keto : enol >99 : 1 in chloroform).…”

“…Most 3-hydroxythiophenes prepared by FVP are reasonably stable compounds that can be stored at À20 1C almost indefinitely, though the 2-methyl derivative is an exception. It is thought to form a dimer 13 though we were unable to confirm this observation. Instead, we found that the parent compound 1 dimerises spontaneously at room temperature or below, either as the neat material or in solution, over a period of a few days.…”

“…Tables of 1 H and 13 C NMR data for the thiophen-3(2H)-one tautomer of a range of derivatives are provided in the ESIw, augmenting some previously reported data. 1 Parameters for thiophen-3(2H)-one 1K itself are shown in Fig.…”

“…3-Hydroxythiophenes-1 H and 13 C NMR spectra 1 H NMR spectroscopic data for a range of 3-hydroxythiophenes (mostly 2,5-disubstituted) have been collated. 1 Tables of 1 H and 13 C NMR data for the 3-hydroxythiophene tautomer of a range of mono-substituted derivatives are provided in the ESIw and data for 3-hydroxythiophene 1E itself are shown in Fig. 1.…”

“…3-Alkoxythiophenes and 3-acetoxythiophenes (see below) have generally similar parameters to their 3-hydroxy analogues (ESIw), though the acetoxy compound 21 shows significant deshielding at H-2 and C-2 with respect to the other compounds. Thiophen-3(2H)-ones-1 H and 13 C NMR spectra…”