CuI-Catalyzed Conjugate Addition of Silyl Boronic Esters: Retracing Catalytic Cycles Using Isolated Copper and Boron Enolate Intermediates
CuI-Catalyzed Conjugate Addition of Silyl Boronic Esters: Retracing Catalytic Cycles Using Isolated Copper and Boron Enolate Intermediates
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DOI：
10.1021/om500989w
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发表时间：
2014-11
期刊：
影响因子：
2.8
通讯作者：
Jacqueline Plotzitzka;C. Kleeberg
中科院分区：
文献类型：
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作者：
Jacqueline Plotzitzka;C. Kleeberg
铜(I)催化的硅基硼酸酯与α，β-不饱和醛、酮和酯的共轭加成反应是人工合成的成熟反应。首次分离和使用中心反应中间体以及作为主要反应产物的硼烯醇酸盐，以在实验基础上推断催化循环。使用NHC CuI络合物作为模型催化剂，可以进行有效的催化转化，并分离和表征形成的铜烯醇络合物作为关键中间体。结果表明，对于该催化体系，O-或C-烯酸的性质对催化过程是至关重要的。对于α，β不饱和的醛和酮，主要生成O-烯酸酯，而对于α，β-不饱和的酯，主要生成C-烯酸酯。O-烯醇铜的催化循环是唯一容易的，因为它们在催化活性的铜-硅物种的形成下与硅基硼酸酯有效地反应。
Copper(I)-catalyzed conjugate additions of silyl boronic esters to α,β-unsaturated aldehydes, ketones, and esters are synthetically well-established reactions. For the first time central reactive intermediates as well as the boron enolates as the primary reaction products are isolated and employed in order to deduce catalytic cycles on an experimental basis. Employing an NHC CuI complex as a model catalyst, it is possible to perform efficient catalytic transformations as well as to isolate and characterize the formed copper enolate complexes as the key intermediates. It is shown that for this catalytic system the nature of this enolate—O- or C-enolate—is crucial for the catalytic process. For α,β-unsaturated aldehydes and ketones the O-enolate is formed predominantly, while for α,β-unsaturated esters the C-enolate is the major product. Catalytic turnover is only facile for copper O-enolates, as they react efficiently with the silyl boronic ester under (re)formation of the catalytically active Cu–Si specie...