Functional derivatives of thiophene

Synthesis of thieno[3.2-b]pyrrolenine derivatives under the Fischer reaction conditions

“…To this end, the pre synthesized hydrazines 6a,b 11 were refluxed with 3 methylbutan 2 one in benzene in a flow of dry hydrogen chloride for 1 h. Indeed, the reac tion gave thienopyrrolenine salts 7a,b, which are stable on storage in air unlike free thienopyrrolenines 2a,b (Scheme 3).…”

“…7631 86 9) (0.060-0.200). Ethyl 4 (2 acetyl hydrazino) 2 methylthiophene 3 carboxylate (1a) 11 4 hydr azino 2 methylthiophene 3 carboxate hydrochlorides 6a,b, 11 and benzothiophenone 8 15 were prepared by known procedures. Commercially available (Merck, Acros, Aldrich) butan 2 one, 3 methylbutan 2 one, trifluoroacetic acid, and p toluene sulfonic acid samples, a 15% solution of butyllithium in hexane, anhydrous (99.9%) zinc chloride, methanol, and benzene were used.…”

“…The organic fractions were combined, washed with water, and concentrated under reduced pressure. After solvent evaporation, the residue was chromatographed on silica gel using a 3 : 1 CH 2 Cl 2 -ethyl acetate mixture as the eluent to give 3.5 g (41%) of 2,3,3 trimethylbenzo[b]thieno [3,2 b]pyrrolenine (11) Methyl iodide (0.55 mL, 8.8 mmol) was added and the mixture was kept for 1.5 h at -70 °C and slowly warmed up to 15 °C. The solution was poured into water and extracted with ether and the residue was chromatographed on silica gel using a 7 : 1 petroleum ether-ethyl acetate mixture as the eluent to give 0.18 g (20%) of compound 11.…”

“…It is noteworthy that the ben zidine rearrangement product 4a has also been isolated in a previous work. 11 In all cases, substantial resinification took place.…”

“…Thienyl hydrazine hydrochloride 6a 11 was isolated in 63% yield and hydrazone 3a was obtained in 42% yield. Compounds 4a and 5a were also formed as side products in the second reaction step.…”