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
The photocatalytic contra-thermodynamic E→Z isomerization of vinyl boronates by using a binaphthol catalyst is disclosed. The reaction, based on the transient formation of a suitable chromophore with a BINOL derivative as the catalyst, allowed geometrical isomerization in good-to-excellent Z/E ratio and excellent-to-quantitative yields. The mechanism of this E→Z contra-thermodynamic isomerization was
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.