Application of the Lithiation−Borylation Reaction to the Preparation of Enantioenriched Allylic Boron Reagents and Subsequent in Situ Conversion into 1,2,4-Trisubstituted Homoallylic Alcohols with Complete Control over All Elements of Stereochemistry
作者:Martin Althaus、Adeem Mahmood、José Ramón Suárez、Stephen P. Thomas、Varinder K. Aggarwal
DOI:10.1021/ja102041s
日期:2010.4.28
Highly Diastereo- and Enantioselective Allylboration of Aldehydes using α-Substituted Allyl/Crotyl Pinacol Boronic Esters via in Situ Generated Borinic Esters
作者:Jack L.-Y. Chen、Helen K. Scott、Matthew J. Hesse、Christine L. Willis、Varinder K. Aggarwal
DOI:10.1021/ja401564z
日期:2013.4.10
Readily available, alpha-substituted allyl/crotyl pinacol boronic esters often give low E/Z selectivity (with Z favored) in reactions with aldehydes. We found that addition of nBuLi to the pinacol boronic ester followed by trapping of the alkoxide with TFAA leads to an intermediate allyl borinic ester which undergoes allylboration with very high E selectivity. The substrate scope includes primary to tertiary alkyl alpha-substituents, crotyl substrates, and the previously unreported beta-methallyl pinacol boronic esters. The latter give very high Z selectivity under standard conditions which is completely reversed to high E selectivity under the new conditions. Monitoring the reaction by B-11 NMR confirmed that the reaction proceeds through a borinic ester intermediate.
Application of the Lithiation−Borylation Reaction to the Preparation of Enantioenriched Allylic Boron Reagents and Subsequent In Situ Conversion into 1,2,4-Trisubstituted Homoallylic Alcohols with Complete Control over All Elements of Stereochemistry
作者:Martin Althaus、Adeem Mahmood、José Ramón Suárez、Stephen P. Thomas、Varinder K. Aggarwal
DOI:10.1021/ja910593w
日期:2010.3.24
of aldehydes gave (Z)-anti-homoallylic alcohols in greater than 95:5 er and 99:1 dr. However, in the special case of the methyl-substituted lithiated carbamate, diamine-free conditions were required to achieve high selectivity. Reactions of sparteine-complexed lithiated carbamates with (Z)-alkenyl pinacol boronic esters and (E)-alkenyl neopentyl boronic esters gave (E)-syn- and (E)-anti-homoallylic
Hoppe 的锂化氨基甲酸酯与乙烯基硼烷和硼酸酯的反应得到烯丙基硼烷/硼酸酯,随后加入醛类为高对映体比率和非对映体比率的对映体富集的高烯丙醇提供了一条新途径。具体而言,sparteine 络合的锂化氨基甲酸酯与反式-链烯基-9-BBN 衍生物的反应,然后加入醛,以大于 95:5 er 和 99:1 dr 的形式生成 (Z)-抗高烯丙醇。然而,在甲基取代锂化氨基甲酸酯的特殊情况下,需要无二胺条件才能实现高选择性。sparteine 络合的锂化氨基甲酸酯与 (Z)-链烯基频哪醇硼酸酯和 (E)-链烯基新戊基硼酸酯的反应分别生成 (E)-syn- 和 (E)-anti-homoallylic 醇, 大于 96: 4 er 和 98:2 博士。在这些反应中,需要路易斯酸 (MgBr(2) 或 BF(3) x OEt(2)) 来促进 1,2-金属酸盐重排和中间烯丙基硼酸酯添加到醛中。该方法为三类高选择性高烯丙醇中的每一种提供了通用途径。