Catalytic enantioselective synthesis of 1-hydroxy-2,3-bisboronate esters through multicomponent borylation/1,2-addition is reported. Catalyst and substrates are readily available, form both a C–B and C–C bond, and generate up to three contiguous stereocenters. The reaction is tolerant of aryl, vinyl, and alkyl aldehydes and ketones in up to 95% yield, >20:1 dr, and 99:1 er. Intramolecular additions to aldehydes and ketones result in stereodivergent processes. The hydroxy bis(boronate) ester products are amenable to site-selective chemical elaboration.
A Cu-catalyzed method for the efficient enantio-and diastereoselective synthesis of chiral homoallylic amines bearing a quaternary carbon and an alkenylboron is disclosed. Transformations are promoted by a readily prepared (phosphoramidite)-Cu complex, and involve bench-stable γ-disubstituted allyldiborons and benzyl imines; products are obtained in up to 82% yield, >20:1 dr, and >99:1 er. Reactions proceed via stereodefined boron-stabilized allylic Cu species formed by an enantioselective transmetalation. Utility of the 1-amino-3-alkenylboronate products is highlighted by a variety of synthetic transformations.
A single-pot Cu-catalyzed enantio-and diastereoselective tandem hydroboration/borylative cyclization of alkynes with ketones for the synthesis of carbocycles is reported. The reaction proceeds via a desymmetrization and generates four contiguous stereocenters, including an allcarbon quaternary center. The method provides rapid access to [6,5]-, [5,5]-bicycles, and cyclopentane products. Catalyst controlled diastereoselectivity by selection of bisphosphine ligand is noted. Utility of the products is demonstrated by site-and chemoselective transformations that afford valuable alkenyl and allyl organoborons.
A general method for the synthesis
of secondary homoallylic alcohols
containing α-quaternary carbon stereogenic centers in high diastereo-
and enantioselectivity (up to >20:1 dr and >99:1 er) is disclosed.
Transformations employ readily accessible aldehydes, allylic diboronates,
and a chiral copper catalyst and proceed by γ-addition of in
situ generated enantioenriched boron-stabilized allylic copper nucleophiles.
The catalytic protocol is general for a wide variety of aldehydes
as well as a variety of 1,1-allylic diboronic esters. Hammett studies
disclose that diastereoselectivity of the reaction is correlated to
the electronic nature of the aldehyde, with dr increasing as aldehydes
become more electron poor.
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