Photochemical intramolecular amination for the synthesis of heterocycles

Green Chem., 2017, Advance Article
DOI: 10.1039/C7GC02261A, Communication

Shawn Parisien-Collette, Corentin Cruche, Xavier Abel-Snape, Shawn K. Collins
Polycyclic heterocycles can be formed in good to excellent yields via photochemical conversion of the corresponding substituted aryl azides under irradiation with purple LEDs in a continuous flow reactor.

Photochemical intramolecular amination for the synthesis of heterocycles

 

Shawn Parisien-Collette,^a  Corentin Cruché,^a  Xavier Abel-Snape^a  and  Shawn K. Collins*^a 

 Author affiliations

*Corresponding authors

^aShawn Parisien-Collette, Corentin Cruché, Xavier Abel-Snape and Prof, Dr Shawn K. Collins, Department of Chemistry and Centre in Green Chemistry and Catalysis, Université de Montréal, CP 6128 Station Downtown, Montréal, Canada H3C 3J7
E-mail: shawn.collins@umontreal.ca

Abstract

Polycyclic heterocycles can be formed in good to excellent yields via photochemical conversion of the corresponding substituted aryl azides under irradiation with purple LEDs in a continuous flow reactor. The experimental set-up is tolerant to UV-sensitive functional groups while affording diverse carbazoles, as well as an indole and pyrrole framework, in short reaction times. The photochemical method is presumed to progress through a mechanism differing from the other methods of azide activation involving transition metal catalysis.

Methyl 9H-carbazole-2-carboxylate (9): Following the Photodecomposition Procedure A, starting from Methyl 2’-azido-[1,1’-biphenyl]-4-carboxylate, the crude mixture was purified by silica gel column chromatography (100 % hexanes → 10 % ethyl acetate in hexanes), to afford the desired product as a white solid (24.3 mg, 72 % yield). Following the Photodecomposition Procedure B, starting from Methyl 2’-azido-[1,1’- biphenyl]-4-carboxylate, the crude mixture was purified by silica gel column chromatography (100 % hexanes → 10 % ethyl acetate in hexanes), to afford the desired product as a white solid (27.7 mg, 82 % yield). NMR data was in accordance with what was previously reported.16
16 Takamatsu, K.; Hirano, K.; Satoh, T.; Miura, M. Org. Lett. 2014, 16, 2892-2895

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4-Isopropyl-9H-carbazole (14): Following the Photodecomposition Procedure A, starting from 2-azido-2’-isopropyl-1,1’-biphenyl, the crude mixture was purified by silica gel column chromatography (100 % hexanes → 10 % ethyl acetate in hexanes), to afford the desired product as a yellow solid (16.6 mg, 53 % yield). Following the Photodecomposition Procedure B, starting from 2-azido-2’-isopropyl-1,1’-biphenyl and using ethyl acetate as the solvant, the crude mixture was purified by silica gel column chromatography (100 % hexanes → 10 % ethyl acetate in hexanes), to afford the desired product as a yellow solid (16.0 mg, 51 % yield).

1H NMR (400 MHz, DMSO-d6) δ = 11.29 (s, 1H), 8.11 (d, J = 8.1 Hz, 1H), 7.50 (d, J = 8.1 Hz, 1H), 7.39-7.31 (m, 3H), 7.19- 7.15 (m, 1H), 7.08-7.03 (m, 1H), 3.92-3.82 (m, 1H), 1.41 (d, J = 6.8 Hz, 6H);

13C NMR (100 MHz, DMSO-d6) δ = 143.9, 140.3, 140.1, 126.0, 125.2, 122.8, 122.2, 119.9, 119.1, 114.9, 111.2, 108.9, 30.2, 22.8 (2C);

HRMS (ESI) m/z calculated for C15H15N [M-H]- 208.1130; found 208.1126.

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