110678-97-2Relevant academic research and scientific papers
Photolysis of 1-Aryl-1,2,3-triazoles; Rearrangement via !H-Azirines
Mitchell, Glynn,Rees, Charles W.
, p. 413 - 422 (2007/10/02)
The preparation and photolysis of a series of 1-(1-naphthyl)-1,2,3-triazoles, (2)-(5), and of 1-(2-methyl-1-naphthyl)-1,2,3-triazoles, (6)-(9), with and without electron-withdrawing groups (CO2R, CONH2, CN, CHO, COPh) in the triazole ring, are described.In the first series, triazoles (3) with two electron-withdrawing groups, and triazoles (4) with one such group at C-4, mostly give good yields of the expected benzindoles (10) and 11 respectively.Triazoles (5) with the electron-withdrawing group at C-5 also give benzindoles but these are now mixtures of the expected (12) and rearranged indoles (11).Photolysis of the 1-phenyltriazoles (21) and (22) follows the same pattern, those with the electron-withdrawing group at C-5 rearranging to give mixtures of indoles (23) and (24).This is explained by a mechanism (Scheme 3) in which the less stable carbene intermediate (13) rearranges to the more stable carbene (15) via the 1H-azirine (14), in competition with its direct cyclisation.This provides the first evidence for antiaromatic 1H-azirines as intermediates in a photochemical reaction.Photolysis of the 2-methylnaphthyl compounds follows a different path: diester (7b) and dinitrile (7d) give high yields of the deeply coloured 9-methyl-1H-benzoquinoline derivatives (25a) and (25b) respectively, the first stable examples of this ring system to be isolated.Photolysis of the nitrile (8c) gives 9b-methyl-9bH-benzindole-3-carbonitrile (28), a rare example of a stable indole with a ring junction substituent. 1,2-Shifts in the carbenes are only observed with the bis(trimethylsilyl)triazoles (2d) and (6f), in keeping with the known rapid migration of trimethylsilyl groups to carbene centres.
