CC BY-NC-ND 4.0 · Synlett
DOI: 10.1055/a-1304-4575
letter

N-Arylbenzo[b]phenothiazines as Reducing Photoredox Catalysts for Nucleophilic Additions of Alcohols to Styrenes: Shift towards Visible Light

Fabienne Seyfert
,
This work was financially supported by the Deutsche Forschungsgemeinschaft (DFG, grant Wa 1386/16-2). Financial support by the Karlsruhe Institute of Technology (KIT) is gratefully acknowledged.


Abstract

N-Phenylphenothiazines are an important class of photoredox catalysts because they are synthetically well accessible, they allow the tuning of the optoelectronic properties by different substituents, and they have strong reduction properties for activation of alkenes. One of the major disadvantages of N-phenylphenothiazines, however, is the excitation at 365 nm in the UV-A light range. We synthesized three differently dialkylamino-substituted N-phenylbenzo[b]phenothiazines as alternative photoredox catalysts and applied them for the nucleo­philic addition of alkohols to α-methyl styrene. The additional benzene ring shift the absorbance bathochromically and allows performing the photocatalyses by excitation at 385 nm and 405 nm. This type of photoredox catalysis tolerates other functional groups, as representatively shown for alcohols as substrates with C–C and C–N triple bonds.

Supporting Information



Publication History

Received: 29 September 2020

Accepted: 05 November 2020

Publication Date:
05 November 2020 (online)

© 2020. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial-License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/)

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  • 18 Experimental Procedure Compound 11 (250 mg, 1.00 mmol, 1.00 equiv), 4-bromo-N,N-diisobutylaniline (299 mg, 1.05 mmol, 1.05 equiv), NaOt-Bu (240 mg, 2.50 mmol, 2.50 equiv), tricyclohexylphosphine (20 mg, 0.07 mmol, 0.07 equiv), and Pd2dba3 (46.0 mg, 0.05 mmol, 0.05 equiv) were dissolved in anhydrous toluene (0.26 M). The reaction mixture was stirred under reflux and inert atmosphere overnight and cooled to r.t. The solvent was removed under vacuum. Compound 3 was purified by column chromatography (hexane, silica, Rf = 0.3) and obtained as white solid (256 mg, 0.566 mmol, 56%). 1H NMR (500 MHz, CDCl3): δ = 7.51 (d, J = 7.0 Hz, 1 H), 7.43 (s, 1 H), 7.35 (d, J = 7.10 Hz, 1 H), 7.22–7.14 (m, 4 H), 7.02 (d, J = 7.25 Hz, 1 H), 6.90–6.75 (m, 4 H), 6.51 (s, 1 H), 6.32 (d, J = 8.10 Hz, 1 H), 3.25 (d, J = 7.21 Hz, 4 H), 2.20 (hept, J = 6.70 Hz, 2 H), 0.99 (d, J = 6.55 Hz, 12 H) ppm. 13C NMR (126 MHz, CDCl3): δ = 148.09, 144.11, 142.68, 133.39, 131.31, 130.09, 128.06, 126.96, 126.89, 126.39, 126.21, 125.84, 124.24, 123.97, 122.30, 121.59, 118.97, 116.31, 113.89, 110.91, 60.65, 26.57, 20.67 ppm. ESI-HRMS: m/z calcd: 452.2286 [M+]; found: 452.2269 [M+].
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