A novel Cu-catalyzed diastereo- and enantioselective desymmetrization of cyclopropenes to afford nonracemic cyclopropylboronates is described. Trapping the cyclopropylcopper intermediate with electrophilic amines allows for the synthesis of cyclopropylaminoboronic esters and demonstrates the potential of the approach for the synthesis of functionalized cyclopropanes.
The intermolecular gold(I)-catalyzed
reaction between arylalkynes
and alkenes leads to cyclobutenes by a [2 + 2] cycloaddition, which
takes place stepwise, first by formation of cyclopropyl gold(I) carbenes,
followed by a ring expansion. However, 1,3-butadienes are also formed
in the case of ortho-substituted arylalkynes by a
metathesis-type process. The corresponding reaction of alkenes with
aryl-1,3-butadiynes, ethynylogous to arylalkynes, leads exclusively
to cyclobutenes. A comprehensive mechanism for the gold(I)-catalyzed
reaction of alkynes with alkenes is proposed on the basis of density
functional theory calculations, which shows that the two pathways
leading to cyclobutenes or dienes are very close in energy. The key
intermediates are cyclopropyl gold(I) carbenes, which have been independently
generated by retro-Buchner reaction from stereodefined 1a,7b-dihydro-1H-cyclopropa[a]naphthalenes.
Herein, we report a catalytic and stereospecific method for the preparation of enantioenriched a-hydroxy cyclopropylboronates with control in four contiguous stereocenters. The reaction involves the borylation of readily available allylic epoxides using an inexpensive Cu(I) salt and a commercially available phosphine ligand. High diastereocontrol is achieved and different diastereomers can be selectively prepared. Functionalization of the carbon-boron bond provides access to different enantiomerically enriched trisubstituted cyclopropanes from a common intermediate.
Chiral α-allenols are prepared with high diastereocontrol through an unprecedented and spontaneous β-oxygen elimination of an α-epoxy vinyl boronate. Stochiometric experiments and DFT calculations support a dual role of the copper catalyst, which orchestrates the hydroboration and the syn-elimination step.
We present an efficient strategy for the formal 1,4-reduction of vinyl epoxides that does not require superstoichiometric amounts of a strong reductant. Using a readily available copper catalyst and a diboron compound, a wide variety of enantioenriched allylic alcohols has been prepared. Additionally, epoxyenynes have been reduced in a 1,4-manner to selectively afford skipped enynes or skipped dienes.
Esta es la versión de autor del artículo publicado en: This is an author produced version of a paper published in: Abstract: The copper-catalyzed hydro-and carboboration of strain alkenes is presented. The reaction is highly diastereoselective and affords boronic ester derivatives many of which are difficult to synthesize by known methods.Competition experiments with different alkenes show that high levels of chemoselectivity can be achieved. DFT calculations are in agreement with the observed chemoselectivity.
Herein, we report a catalytic and stereospecific method for the preparation of enantioenriched a-hydroxy cyclopropylboronates with control in four contiguous stereocenters. The reaction involves the borylation of readily available allylic epoxides using an inexpensive Cu(I) salt and a commercially available phosphine ligand. High diastereocontrol is achieved and different diastereomers can be selectively prepared. Functionalization of the carbon-boron bond provides access to different enantiomerically enriched trisubstituted cyclopropanes from a common intermediate.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.