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.