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. 2017 Nov 20;56(47):15136-15140.
doi: 10.1002/anie.201709690. Epub 2017 Oct 24.

A Lewis Base Catalysis Approach for the Photoredox Activation of Boronic Acids and Esters

Fabio Lima  1 , Upendra K Sharma  2 , Lars Grunenberg  1 , Debasmita Saha  2 , Sandra Johannsen  1 , Joerg Sedelmeier  3 , Erik V Van der Eycken  2   4 , Steven V Ley  1
Affiliations

A Lewis Base Catalysis Approach for the Photoredox Activation of Boronic Acids and Esters

Fabio Lima et al. Angew Chem Int Ed Engl. .

Abstract

We report herein the use of a dual catalytic system comprising a Lewis base catalyst such as quinuclidin-3-ol or 4-dimethylaminopyridine and a photoredox catalyst to generate carbon radicals from either boronic acids or esters. This system enabled a wide range of alkyl boronic esters and aryl or alkyl boronic acids to react with electron-deficient olefins via radical addition to efficiently form C-C coupled products in a redox-neutral fashion. The Lewis base catalyst was shown to form a redox-active complex with either the boronic esters or the trimeric form of the boronic acids (boroxines) in solution.

Keywords: Lewis base catalysis; boronic acids; cross-coupling; photoredox catalysis; synthetic methods.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Photoredox activation of organoboron reagents. LB=Lewis base.
Scheme 2
Scheme 2
Optimized reaction conditions for the Giese‐type addition of boronic ester 1 a to acrylate 2 a, highlighting the results obtained with selected Lewis base catalysts. The optimization was conducted with 0.1 mmol of 1 a and 0.4 mmol of 2 a. Yields of 3 aa determined by 1H NMR analysis of the crude reaction mixture with CH2Br2 as an internal standard. Yield of isolated product given in parentheses.
Scheme 3
Scheme 3
Scope with electron‐deficient alkenes. Yields of isolated products are given. Ar=4‐MeOC6H4. Reaction conditions: 1 a (0.2 mmol), 2 a–2 r (0.4–0.8 mmol), PC(1) (2 mol %), quinuclidin‐3‐ol (20 mol %), irradiation supplied by a commercial blue LED strip (14.4 W at 450 nm).
Scheme 4
Scheme 4
Scope with boronic pinacol esters. Yields of isolated products are given. Reaction conditions: 1 a–1 q (0.2 mmol), 2 d (0.8 mmol), PC(1) (2 mol %), LB (20 mol %), irradiation supplied by a commercial blue LED strip (14.4 W at 450 nm). * Yield determined by 1H NMR analysis of the crude reaction mixture with CH2Br2 as an internal standard.
Scheme 5
Scheme 5
Scope with boronic acids. Yields of isolated products are given. Reaction conditions: 4 a–4 s (0.2 mmol), 2 d (0.8 mmol), PC(1) (2 mol %), LB (20 mol %), irradiation supplied by a commercial blue LED strip (14.4 W at 450 nm).
Scheme 6
Scheme 6
Possible mechanism for the Lewis base and photoredox catalyzed Giese‐type addition of boronic acid derivatives.
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References

    1. None
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    1. None

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