Boron Carboxylate Catalysis of Homoallylboration

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• 作者：Gabrielle J. Dugas ; Yu-hong Lam ; K. N. Houk ; Isaac J. Krauss
• 刊名：Journal of Organic Chemistry
• 出版年：2014
• 出版时间：May 16, 2014
• 年：2014
• 卷：79
• 期：10
• 页码：4277-4284
• 全文大小：535K
• 年卷期：v.79,no.10(May 16, 2014)
• ISSN：1520-6904

文摘

Boron tris(trifluoroacetate) is identified as the first effective catalyst for the homoallyl- and homocrotylboration of aldehydes by cyclopropylcarbinylboronates. NMR spectroscopic studies and theoretical calculations of key intermediates and transition states both suggest that a ligand-exchange mechanism, akin to our previously reported PhBCl₂-promoted homoallylations, is operative. Our experimental and theoretical results also suggest that the catalytic activity of boron tris(trifluoroacetate) might originate from more facile catalytic turnover of the trifluoroacetate ligands (in agreement with DFT calculations) or from a lower propensity for formation of off-pathway reservoir intermediates (as observed by ¹H NMR). This work shows that carboxylates are viable catalytic ligands for homoallyl- and homocrotylations of carbonyl compounds and opens the door to the development of catalytic asymmetric versions of this transformation.