Catalysis of an S2 pathway by geometric preorganization.

Bimolecular nucleophilic substitution (S2) mechanisms occupy a central place in the historical development and teaching of the field of organic chemistry. Despite the importance of S2 pathways in synthesis, catalytic control of ionic S2 pathways is rare and notably uncommon even in biocatalysis, reflecting the fact that any electrostatic interaction between a catalyst and the reacting ion pair necessarily stabilizes its charge and, by extension, reduces polar reactivity. Nucleophilic halogenase enzymes navigate this tradeoff by desolvating and positioning the halide nucleophile precisely on the S2 trajectory, using geometric preorganization to compensate for the attenuation of nucleophilicity.

Copper-Catalyzed Coupling of Alkyl Vicinal Bis(boronic Esters) to an Array of Electrophiles.

A neighboring boronate group in the substrate provides a dramatic rate acceleration in transmetalation to copper and thereby enables organoboronic esters to participate in unprecedented site-selective cross-couplings. This cross-coupling operates under practical experimental conditions and allows for coupling between vicinal bis(boronic esters) and allyl, alkynyl, and propargyl electrophiles as well as a simple proton. Because the reactive substrates are vicinal bis(boronic esters), the cross-coupling described herein provides an expedient new method for the construction of boron-containing reaction products from alkenes.

Enantiomerically Enriched α-Borylzinc Reagents by Nickel-Catalyzed Carbozincation of Vinylboronic Esters.

In this paper is described a synthesis of enantiomerically enriched, configurationally stable organozinc reagents by catalytic enantioselective carbozincation of a vinylboronic ester. This process furnishes enantiomerically enriched α-borylzinc intermediates that are shown to undergo stereospecific reactions, producing enantioenriched secondary boronic ester products. The properties of the intermediate α-borylzinc reagent are probed and the synthetic utility of the products is demonstrated by application to the synthesis of (-)-aphanorphine and (-)-enterolactone.

Recent Advances in Radical Addition to Alkenylboron Compounds.

The addition of carbon-centered radicals to alkenylboron compounds provides a useful method for the construction of organoboron reagents which are versatile reagents in chemical synthesis. While the first examples of this type or process appeared 70 years ago, until recently, attention to this type of reaction has been limited. A number of examples of this reactivity have been demonstrated recently, and strategies are emerging that allow for tuning the reagent structure in order to modulate reactivity.

Enantioselective Radical Addition/Cross-Coupling of Organozinc Reagents, Alkyl Iodides, and Alkenyl Boron Reagents.

A hybrid transition-metal/radical process is described that results in the addition of organozinc reagents and alkyl halides across alkenyl boron reagents in an enantioselective catalytic fashion. The reaction can be accomplished both intermolecularly and intramolecularly, providing useful product yields and high enantioselectivities in both manifolds.

Vinylidenation of Organoboronic Esters Enabled by a Pd-Catalyzed Metallate Shift.

Organoboron "ate" complexes undergo a net vinyl insertion reaction to give 1,1-disubstituted alkenyl boronic esters when treated with stoichiometric allyl acetate and a palladium catalyst. Reactions that employ vinyllithium afforded good to excellent yields after one hour, while reactions that employ vinylmagnesium chloride furnished modest to good yields after 18 hours.

Enantioselective Construction of Tertiary Boronic Esters by Conjunctive Cross-Coupling.

Catalytic enantioselective conjunctive cross-coupling has been developed to construct tertiary alkylboronic esters. These reactions occur with good yield and enantioselectivity for a range of substrates. Mechanistic experiments reveal aspects of the catalytic cycle that allow hindered substrates to react without significant complicating side reactions.

Ni-Catalyzed Enantioselective Conjunctive Coupling with C(sp) Electrophiles: A Radical-Ionic Mechanistic Dichotomy.

The catalytic enantioselective conjunctive coupling of C(sp) electrophiles can be accomplished with Ni catalysis. The enantioselectivity of the reaction is dependent on reaction mechanism with many substrates able to engage in an asymmetric process with Pybox-Ni complexes, whereas other substrates provide racemic product mixtures. The link between substrate structure and selectivity is addressed.

Pd-Catalyzed Conjunctive Cross-Coupling between Grignard-Derived Boron "Ate" Complexes and C(sp) Halides or Triflates: NaOTf as a Grignard Activator and Halide Scavenger.

Catalytic enantioselective conjunctive cross-couplings that employ Grignard reagents are shown to furnish an array of nonracemic chiral organoboronic esters in an efficient and highly selective fashion. The utility of sodium triflate in facilitating this reaction is two-fold: it enables "ate" complex formation and overcomes catalytic inhibition by halide ions.

Catalytic conjunctive cross-coupling enabled by metal-induced metallate rearrangement.

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.

Two BN isosteres of anthracene: synthesis and characterization.

The synthesis of two parental BN anthracenes, 1 and 2, was developed, and their electronic structure and reactivity behavior were characterized in direct comparison with all-carbon anthracene. Gas-phase UV-photoelecton spectroscopy studies revealed the following HOMO energy trend: anthracene, -7.4 eV; BN anthracene 1, -7.