Abstract
AbstractThe synthesis of alkyl boronic esters by direct decarboxylative radical addition of carboxylic acids to vinyl boronic esters is described. The reaction proceeds under mild photoredox catalysis and involves an unprecedented single‐electron reduction of an α‐boryl radical intermediate to the corresponding anion. The reaction is amenable to a diverse range of substrates, including α‐amino, α‐oxy, and alkyl carboxylic acids, thus providing a novel method to rapidly access boron‐containing molecules of potential biological importance.
Highlights
Boronic acids and their derivatives occupy a central position in the chemical sciences,[1] with broad applications in synthesis,[2] polymer chemistry,[3] and as chemical receptors.[4]
They play an increasingly important role in medicinal chemistry since they can act as carboxylic acid bioisosteres.[5]
Peptidyl boronic acids can function as inhibitors of serine proteases, an attribute that has led to the commercialization of the antineoplastic drug, bortezomib, for the treatment of relapsed and refractory multiple myeloma (Scheme 1 a).[6]
Summary
DMF none [a] All reactions were carried out with 1 (0.050 mmol), 2 (0.075 mmol), Cs2CO3 (0.050 mmol), the photocatalyst (0.50 mmol), and solvent (1.0 mL). [b] Determined by GC using 1,2,4-trimethoxybenzene as an internal standard. [c] Using 5.0 mol % of the photocatalyst D. [d] Reaction performed without Cs2CO3. DMF none [a] All reactions were carried out with 1 (0.050 mmol), 2 (0.075 mmol), Cs2CO3 (0.050 mmol), the photocatalyst (0.50 mmol), and solvent (1.0 mL). Efficiency, with 3 being formed in 82 % yield (entry 8). The use of the organic photocatalyst 4CzIPN (D) under the optimized reaction conditions afforded 3 in 66 % yield, demonstrating that D is a viable alternative to the iridium photocatalyst (entry 9).[16] control experiments were performed to confirm the essential roles of the base, photocatalyst, and light (entries 10–12). [a] Reactions were carried out on a 0.30 mmol scale with irradiation times of between 30 and 72 h. Yields are of isolated products after chromatographic purification. [b] Reactions were carried out on a 0.20 mmol scale.
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