Catalytic Enantioselective Three-Component Hetero-[4+2] Cycloaddition/Allylboration Approach to α-Hydroxyalkyl Pyrans: Scope, Limitations, and Mechanistic Proposal
作者:Xuri Gao、Dennis G. Hall、Michael Deligny、Annaick Favre、François Carreaux、Bertrand Carboni
DOI:10.1002/chem.200501197
日期:2006.4.3
hetero-[4+2] cycloaddition/allylboration reaction between 3-boronoacrolein, enol ethers, and aldehydes to afford alpha-hydroxyalkyl dihydropyrans. The key substrate, 3-boronoacrolein pinacolate (2) was found to be an exceptionally reactive heterodiene in the hetero-[4+2] cycloaddition catalyzed by Jacobsen's chiral Cr(III) catalyst 1. The scope and limitations of this process were thoroughly examined
本文介绍了3-硼诺丙烯醛,烯醇醚和醛之间的催化对映选择性三组分杂[4 + 2]环加成/烯丙基化反应的设计和优化,以提供α-羟烷基二氢吡喃。发现关键底物3-硼烷丙烯醛频哪酸酯(2)是由雅各布森手性Cr(III)催化剂1催化的杂[4 + 2]环加成反应中的一种异常反应性杂二烯。对该方法的范围和局限性进行了彻底的研究。 。以高收率和超过95%的对映选择性得到3-硼诺丙烯醛松油酸酯和乙基乙烯基醚的加合物。这种环状的α-手性烯丙基硼酸酯增加了各种各样的醛底物,包括不饱和醛和α-手性醛,从而得到非对映体纯的产物。可以使用无环的2-取代的烯醇醚,在这种情况下,催化剂促进了动力学选择反应,该反应使Z烯醇醚优于E异构体。令人惊讶地,发现3-(硼烷醛)松果酸酯是优于(E)-4-氧代丁烯酸乙酯的杂二烯,并提出了基于可能的[5 + 2]过渡态的机理解释。