title: Thermally Induced Denitrogenative Annulation for the Synthesis of Dihydroquinolinimines and Chroman-4-imines.
abstract: A rapid growth in synthetic methods for the preparation of diverse organic molecules using N-sulfonyl-1,2,3-triazoles is of great interest in organic synthesis. Transition metals are generally used to activate the α-imino diazo intermediates. Metal-free methods have not been studied in detail, but can be a good complement to transition metal catalysis in the mild reaction conditions. We herein report a novel method for the preparation of 2,3-dihydroquinolin-4-imine and chroman-4-imine analogs from their corresponding N-sulfonyl-1,2,3-triazoles in the absence of metal catalysts. To achieve intramolecular annulation, the introduction of an electron-donating group is required at the meta position of N-sulfonyl-1,2,3-triazole methyl anilines. The inclusion of tailored substituents on the aniline moieties and nitrogen atoms enhances the nucleophilicity of the phenyl π-electrons, thus allowing them to undergo a Friedel-Crafts-type reaction with the highly electrophilic ketenimines. This metal-free method was carefully optimized to generate a variety of dihydroquinolin-4-imines and chroman-4-imines in moderate-to-good yields.
authors.affiliation: Department of Chemistry, Nation Sun Yat-sen University, 70 Lienhai Rd., Kaohsiung, 80424, Taiwan.
authors.forename: Chih-Hung
authors.initials: CH
authors.lastname: Chou
authors.affiliation: Department of Chemistry, Nation Sun Yat-sen University, 70 Lienhai Rd., Kaohsiung, 80424, Taiwan.
authors.forename: Ying-Yu
authors.initials: YY
authors.lastname: Chen
authors.affiliation: Department of Chemistry, Nation Sun Yat-sen University, 70 Lienhai Rd., Kaohsiung, 80424, Taiwan.
authors.forename: Basker
authors.initials: B
authors.lastname: Rajagopal
authors.affiliation: Department of Chemistry, Nation Sun Yat-sen University, 70 Lienhai Rd., Kaohsiung, 80424, Taiwan.
authors.forename: Hsiu-Chung
authors.initials: HC
authors.lastname: Tu
authors.affiliation: Department of Chemistry, Nation Sun Yat-sen University, 70 Lienhai Rd., Kaohsiung, 80424, Taiwan.
authors.forename: Kuan-Lin
authors.initials: KL
authors.lastname: Chen
authors.affiliation: Department of Chemistry, Nation Sun Yat-sen University, 70 Lienhai Rd., Kaohsiung, 80424, Taiwan.
authors.forename: Sheng-Fu
authors.initials: SF
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Nation Sun Yat-sen University, 70 Lienhai Rd., Kaohsiung, 80424, Taiwan.
authors.forename: Chien-Fu
authors.initials: CF
authors.lastname: Liang
authors.affiliation: Department of Medical Imaging and Radiological Sciences, Kaohsiung Medical University, 100, Shih-Chuan 1st Rd., Kaohsiung, 80708, Taiwan.
authors.forename: Yu-Chang
authors.initials: YC
authors.lastname: Tyan
authors.affiliation: Department of Chemistry, Nation Sun Yat-sen University, 70 Lienhai Rd., Kaohsiung, 80424, Taiwan. pclin@mail.nsysu.edu.tw.
authors.forename: Po-Chiao
authors.initials: PC
authors.lastname: Lin
mesh_terms: D002839:Chromans / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D007097:Imines / Q000138:chemical synthesis* / Q000737:chemistry; D008958:Models, Molecular; D011804:Quinolines / Q000138:chemical synthesis* / Q000737:chemistry; D013457:Sulfur Compounds / Q000737:chemistry; D013696:Temperature; D014230:Triazoles / Q000737:chemistry*
chemical_list: C544515:1,4-dihydroquinoline; D002839:Chromans; D007097:Imines; D011804:Quinolines; D013457:Sulfur Compounds; D014230:Triazoles
keywords: annulation; carbenes; cyclization; diazo compounds; ketenimines