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

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.

Photoredox‐Catalyzed Cyclobutane Synthesis by a Deboronative Radical Addition–Polar Cyclization Cascade

“…Interestingly, replacement of arylboronate complex 5 with the corresponding trifluoroborate (entry 13) or a combination of 6 and DMAP (entry 14) failed to give either cyclobutane 8 or the Giese product 9 . Furthermore, submitting enoate 7 a to the optimized Giese reaction conditions reported by Akita (with BF 3 K salt) and Ley (with Bpin and DMAP) resulted in no cyclobutane formation . These results highlight the benefits on reactivity of using easily oxidized arylboronate complexes such as 5 .…”

Accessing 1,2‐Substituted Cyclobutanes through 1,2‐Azaborine Photoisomerization

“…Additional C−B bond functionalizations can be performed with the secondary aminoborylated cyclobutane 5 . For example, compound 5 can be alkylated with methyl vinyl ketone in the presence of an Ir catalyst under photoredox conditions to produce 9 (Scheme a) . Compound 5 can also be fluorinated stereoselectively with Selectfluor (Scheme b) .…”

Advances in the Synthesis of Imine‐Containing Azaarene Derivatives via Photoredox Catalysis

“…Subsequently, the groups of Rueping, [20] Ravelli, [21] Ley [22] and so on [23] subsequently reported conjugate additions of diverse radicals to vinylazaarenes by using different photocatalytic methods (Scheme 7). Among them, Ravelli exploited a hydrogen-atom-transfer (HAT) catalytic strategy to form radical intermediates, but the use of vinylazaarenes as the substrates in these transformations will be discussed herein.…”

“…In the same year, the Ley group described the employment of a dual catalytic system comprising a Lewis base catalyst and a photoredox catalyst to generate carbon radicals from either boronic acids or esters, which were added to various electrondeficient olefins (Scheme 7C). [22] Although most olefins were activated by ketones or esters, they also tested 2-vinylpyridine (12 a), 4-vinylpyridine (12 b) and 2-(1-phenylvinyl)pyridine 35 a in the reaction with boronic ester 38 using 2.0 mol% Ir[dF(CF 3 ) ppy] 2 (dtbbpy)PF 6 as a photoredox catalyst and 20 mol% quinuclidin-3-ol as a Lewis base catalyst at 30°C. Products 39 were obtained in 42 to 77 % yields.…”