The direct amination of alkyl and aryl pinacol boronates is accomplished with lithiated methoxyamine. This reaction directly provides aliphatic and aromatic amines, stereospecifically, and without preactivation of the boronate substrate.
A general method is introduced for the rapid and simultaneous evaluation of each member of large encoded catalyst libraries for the ability to catalyze a reaction in solution. The procedure was used to select active catalysts from a library of potential polymer-bound multifunctional catalysts. From approximately 7000 beads screened (3150 distinct catalysts), 23 beads were selected for catalysis of an acylation reaction. Kinetic experiments indicate that the most strongly selected beads are also the most efficient catalysts.
The reaction of 1,1-bis(pinacolboronate)
esters with alkyl halides
can be effected by metal alkoxides and provides a strategy for the
construction of organoboronate compounds. The reaction is found to
occur by alkoxide-induced deborylation and generation of a boron-stabilized
carbanion.
Terminal alkenes are readily available functional groups that appear in α-olefins produced by chemical industry, and they appear in the products of many contemporary synthetic reactions. While the organic transformations that apply to such alkenes are amongst the most studied reactions in all of chemical synthesis, the number of reactions that apply to nonactivated terminal alkenes in a catalytic enantioselective fashion is small in number. This Review highlights the cases where stereocontrol in catalytic reactions of 1-alkenes is high enough to be useful for asymmetric synthesis.
Transition metal catalysis plays a central role in contemporary organic synthesis. Considering the tremendously broad array of transition-metal-catalyzed transformations, it is remarkable that the underlying elementary reaction steps are relatively few in number. Here we describe an alternative to the organometallic transmetallation step that is common in many metal-catalyzed reactions such as Suzuki-Miyaura coupling. Specifically, we demonstrate that vinyl boronic ester ate complexes, prepared by combining organoboronates and organolithium reagents, engage in Pd-induced metallate rearrangement wherein 1,2-migration of an alkyl or aryl group from boron to the vinyl α-carbon occurs concomitantly with C-Pd σ-bond formation. This elementary reaction enables a powerful cross-coupling reaction in which a chiral palladium catalyst merges three simple starting materials – an organolithium, an organoboronic ester, and an organotriflate – into chiral organoboronic esters with high enantioselectivity.
A highly stereoselective boron-Wittig reaction between stable and readily accessible 1,1-bis(pinacolboronates) and aldehydes furnishes a variety of synthetically useful di- and trisubstituted vinyl boronate esters.
Catalytic
enantiotopic-group-selective cross-couplings of achiral
geminal bis(pinacolboronates) provide a route for the construction
of nonracemic chiral organoboronates. In the presence of a chiral
monodentate taddol-derived phosphoramidite ligand, these reactions
occur with high levels of asymmetric induction. Mechanistic experiments
with chiral 10B-enriched geminal bis(boronates) suggest
that the reaction occurs by a stereochemistry-determining transmetalation
that occurs with inversion of configuration at carbon.
Amongst prospective starting materials for organic synthesis, terminal (monosubstituted) alkenes are ideal. In the form of α-olefins, they are manufactured on enormous scale and they are the core product features from many organic chemical reactions. While their latent reactivity can easily enable hydrocarbon chain extension, alkenes also have the attractive feature of being stable in the presence of many acids, bases, oxidants and reductants. In spite of these impressive attributes, relatively few catalytic enantioselective transformations have been developed that transform aliphatic α-olefins in >90% ee and, with the exception of site-controlled isotactic polymerization of α-olefins,1 none of these processes result in chain-extending C-C bond formation to the terminal carbon.2, 3, 4, 5, 6 Herein, we describe a strategy that directly addresses this gap in synthetic methodology and present a single-flask catalytic enantioselective conversion of terminal alkenes into a range of chiral products. These reactions are enabled by an unusual neighboring group participation effect that accelerates Pd-catalyzed cross-coupling of 1,2-bis(boronates) relative to nonfunctionalized alkyl boronate analogs. In tandem with enantioselective diboration, this reactivity feature connects abundant alkene starting materials to a diverse array of chiral products. Importantly with respect to synthesis utility, the tandem diboration/cross-coupling reaction (DCC reaction) generally provides products in high yield and high selectivity (>95:5 enantiomer ratio), employs low loadings (1–2 mol %) of commercially available catalysts and reagents, it offers an expansive substrate scope, and can address a broad range of alcohol and amine synthesis targets, many of which cannot be easily addressed with current technology.
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