Stereoselective Synthesis of Trisubstituted Alkenylboron Reagents by Boron-Wittig Reaction of Ketones
作者:Sheila Namirembe、Chenpeng Gao、Ryan P. Wexler、James P. Morken
DOI:10.1021/acs.orglett.9b01663
日期:2019.6.7
Application of the boron-Wittigreaction to ketone electrophiles provides a straightforward route to trisubstituted alkenylboronic esters. With either a pentamethyldiethylenetriamine or trimethyl-1,4,7-triazacyclononane additive, the olefination can occur with very high levels of stereocontrol and in good chemical yield.
The carboboration of terminal alkynes was studied with a N‐heterocyclic carbene‐capped α‐cyclodextrin copper(I) complex as catalyst. The intermolecular reaction with CH3I gave linear (L) vinyl boron isomers with high selectivity. The intramolecular reaction with terminal alkynes led to exocyclic vinyl boronates and to an unexpected endocyclic (Z)‐isomer, suggesting an unusual mechanism promoted by
Copper-Catalyzed Asymmetric Reduction of β,β-Disubstituted Alkenylboramides
作者:Yeji Park、Jaesook Yun
DOI:10.1021/acs.orglett.9b03400
日期:2019.11.1
A highly enantioselective copper-catalyzed reduction of β,β-disubstituted alkenylboron compounds was developed using hydrosilane. The copperhydride catalyst coordinated with chiral Josiphos ligand efficiently discriminated β-geminal substituents to generate corresponding β-chiral alkylboramides with excellent enantioselectivities up to 99% ee. The enantioselective reduction protocol provides a facile
Copper(I)-Catalyzed Formal Carboboration of Alkynes: Synthesis of Tri- and Tetrasubstituted Vinylboronates
作者:Ricardo Alfaro、Alejandro Parra、José Alemán、José Luis García Ruano、Mariola Tortosa
DOI:10.1021/ja307670k
日期:2012.9.19
The first copper-catalyzed formal carboboration of alkynes, in which a C-B bond and a C-C bond are created in a single catalytic cycle, is presented. The reaction proceeds with high regioselectivity and syn-stereoselectivity to form tri- and tetrasubstituted vinylboronic esters from commercially available bis-(pinacolato)diboron. A subsequent cross-coupling reaction gives access to highly substituted alkenes.