113649-24-4Relevant academic research and scientific papers
Thiophene Derivatives from Methyl 2-Siloxycyclopropanecarboxylates by Novel 1,3- and 1,2-Sigmatropic Rearrangements
Brueckner, Christiane,Reissig, Hans-Ulrich
, p. 465 - 470 (2007/10/02)
Ester enolates, generated with LDA from methyl 2-siloxycyclopropanecarboxylates 1, and carbon disulfide/methyl iodide afford methyl dihydrothiophenecarboxylates 3.Depending on the substitution pattern, these can be converted into methyl 3-thiophenecarboxylates 7 either by F3B-OEt2-promoted Wagner-Meerwein shift of an alkyl group or by acid-induced elimination of trimethylsilanol.The mechanism of this surprising ring enlargement of cyclopropanes leading to heterocycles is described as an anionic 1,3-sigmatropic rearrangement (10-->11) which even takes place at -78 deg C.Similar reaction conditions convert methyl cyclopropanecarboxylate 13, having no siloxy function, into the γ,δ-unsaturated dithiocarboxylate 14.For its formation an anionic homo-1,5-sigmatropic hydrogen shift is suggested as the key step.On the other hand, methyl 2,2-diphenylcyclopropanecarboxylate (17) affords the ring opening product 19, which must be formed by deprotonation at C-3 of an intermediate cyclopropane derivative.
