Latent Carbene: Diaminomethylation of Thiophenes

• Published in: European journal of organic chemistry 2022-10, Vol.2022 (40), p.n/a
• Main Authors: Koidan, Georgyi, Hurieva, Anastasiya, Zahorulko, Serhii, Zadorozhny, Alexander, Lysenko, Viacheslav, Shvydenko, Tetiana, Rusanov, Eduard B., Kostyuk, Aleksandr
• Format: Article
• Language: English
• Subjects: Aldehydes; Aminal; Carbene insertion; Halogens; Hydrogen bonds; Silylformamidine; Substitutes; Thiophene; Thiophene carbaldehydes; Thiophenes
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.202201048

The reaction of silylformamidine with various halo‐ and ethoxycarbonyl substituted thiophenes was studied. It proceeded via C−H bond insertion of the nucleophilic diaminocarbene that exists in an equilibrium with silylformamidine affording aminals. The reaction proceeded more readily at the 2(5)‐position compared to the 3(4) one. The number of halogens at the thiophenes markedly influences the reaction. The more halogens, the higher the reaction rate. Even one electron acceptor group at the thiophene ring is enough to promote the reaction. As a rule, the reaction does not require solvents or catalysts. Hydrolyses of the aminals provides a novel convenient approach to substituted thiophene aldehydes. Silylformamidine exists in equilibrium with its carbene form. Its reaction with thiophenes bearing at least one electron‐accepting group was studied. Nucleophilic carbene insertion into Csp2−H bond of substituted thiophenes proceeded preferably at the 2(5) positions. Thiophenes featuring halogens at the 2 and 5 positions react much slower at the 3(4) position. A set of aldehyde was prepared. The reaction runs without any solvent or catalyst.