title: Switchable Synthesis of Pyrroles and Pyrazines via Rh(II)-Catalyzed Reaction of 1,2,3-Triazoles with Isoxazoles: Experimental and DFT Evidence for the 1,4-Diazahexatriene Intermediate.
abstract: 4-Aminopyrrole-3-carboxylates and pyrazine-2-carboxylates were synthesized from 5-alkoxyisoxazoles and 1-sulfonyl-1,2,3-triazoles by tuning the Rh(II) catalyst and the reaction conditions. The reaction in chloroform at 100 °C under Rh2(OAc)4catalysis provides 4-aminopyrrole-3-carboxylates in good yields. The use of Rh2(Piv)4in refluxing toluene results in the formation of 1,2-dihydropyrazine-2-carboxylates as the main products, which can be converted by a one-pot procedure to pyrazine-2-carboxylates by heating with catalytic amounts of TsOH. According to the NMR and DFT investigations of the reaction mechanism, pyrroles and dihydropyrazines are formed, respectively, via 1,5- and 1,6-cyclization of common (5Z)-1,4-diazahexa-1,3,5-triene intermediates. The influence of the nature of the catalyst on the product distribution is rationalized in terms of the Rh-catalyzed isomerization of a pyrrolin-2-ylium-3-aminide zwitterion, the primary product of 1,4-diazahexatriene 1,5-cyclization.
authors.affiliation: Institute of Chemistry, St. Petersburg State University , 7/9 Universitetskaya nab., St. Petersburg 199034, Russia.
authors.forename: Nikolai V
authors.initials: NV
authors.lastname: Rostovskii
authors.affiliation: Institute of Chemistry, St. Petersburg State University , 7/9 Universitetskaya nab., St. Petersburg 199034, Russia.
authors.forename: Julia O
authors.initials: JO
authors.lastname: Ruvinskaya
authors.affiliation: Institute of Chemistry, St. Petersburg State University , 7/9 Universitetskaya nab., St. Petersburg 199034, Russia.
authors.forename: Mikhail S
authors.identifier: 0000-0001-5106-4723
authors.initials: MS
authors.lastname: Novikov
authors.affiliation: Institute of Chemistry, St. Petersburg State University , 7/9 Universitetskaya nab., St. Petersburg 199034, Russia.
authors.forename: Alexander F
authors.identifier: 0000-0002-6100-0309
authors.initials: AF
authors.lastname: Khlebnikov
authors.affiliation: Institute of Chemistry, St. Petersburg State University , 7/9 Universitetskaya nab., St. Petersburg 199034, Russia.
authors.forename: Ilia A
authors.initials: IA
authors.lastname: Smetanin
authors.affiliation: Institute of Chemistry, St. Petersburg State University , 7/9 Universitetskaya nab., St. Petersburg 199034, Russia.
authors.forename: Anastasiya V
authors.initials: AV
authors.lastname: Agafonova