Synthesis of arylboronates via Cp*RuCl-catalyzed cycloaddition of alkynylboronates

Ethyl-, vinyl- and ethynylcyanoborates: room temperature borate ionic liquids with saturated and unsaturated hydrocarbon chains

Ethyl-, vinyl- and ethynyltricyano and dicyanofluoroborates were prepared on a gram scale from commercially available potassium trifluoroborates and trimethylsilylcyanide. Salt metathesis resulted in the corresponding EMIm-salts that are hydrophobic room-temperature ionic liquids (RTILs). The new RTILs exhibit unprecedented large electrochemical windows in combination with high thermal stabilities, low dynamic viscosities and high specific conductivities. These properties make them promising materials, especially for electrochemical applications.

Reaction of Alkynyl- and Alkenyltrifluoroborates with Propargyldicobalt Cations: Alkynylation, Alkenylation, and Cyclopropanation Product Pathways

The Lewis acid-mediated Nicholas reactions of propargyl acetate-Co₂(CO)₆ complexes with a series of potassium alkynyltrifluoroborates and potassium alkenyltrifluoroborates are described. Alkynyltrifluoroborates directly alkynylate the intermediate propargyldicobalt cations. In contrast, alkenyltrifluoroborates proceed through one of the three modes of dominant reactivity: C-2-substituted alkenyltrifluorobrates directly alkenylate, predominantly with the retention of stereochemistry. C-1-substituted alkenyltrifluoroborates alkenylate at C-2. Potassium vinyltrifluoroborate incorporates a cyclopropane at the site propargyl to alkynedicobalt. Computational analysis of these systems explains the differential modes of reactivity of alkenyltrifluoroborates and outlines the probable mechanisms for the formation of each product.

Synthesis and reactivity of alkynyl boron compounds

Over the last century, there have been considerable developments in organoboron chemistry due to the stability, non-toxicity, and easy commercial availability of various boronic esters. Several organoboron reagents have emerged and play an increasingly important role in everyday organic synthesis. Among them, alkynyl boron compounds have attracted significant attention due to their easy synthesis and diverse reactivity. In this review, we summarize the advancement of research on alkynyl boron compounds, highlighting their importance in the synthesis of valuable compounds.

Ruthenium-Catalyzed Cycloadditions to Form Five-, Six-, and Seven-Membered Rings

Ruthenium-catalyzed cycloadditions to form five-, six-, and seven-membered rings are summarized, including applications in natural product total synthesis. Content is organized by ring size and reaction type. Coverage is limited to processes that involve formation of at least one C-C bond. Processes that are stoichiometric in ruthenium or exploit ruthenium as a Lewis acid (without intervention of organometallic intermediates), ring formations that occur through dehydrogenative condensation-reduction, σ-bond activation-initiated annulations that do not result in net reduction of bond multiplicity, and photochemically promoted ruthenium-catalyzed cycloadditions are not covered.

Synthesis of Anthraquinones by Iridium-Catalyzed [2 + 2 + 2] Cycloaddition of a 1,2-Bis(propiolyl)benzene Derivative with Alkynes

[2 + 2 + 2] cycloaddition of a 1,2-bis(propiolyl)benzene derivative with terminal and internal alkynes takes place in the presence of [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene) combined with bis(diphenylphosphino)ethane (DPPE) to give anthraquinones in 42% to 93% yields with a simple experimental procedure. A fluorenone derivative can also be synthesized by iridium-catalyzed [2 + 2 + 2] cycloaddition of a benzene-linked ketodiyne with an internal alkyne to give a 94% yield.

Synthesis and chemoselective ligations of MIDA acylboronates with O-Me hydroxylamines

A chemoselective amide-bond forming ligation of N-methyliminodiacetyl (MIDA) acylboronates and O-Me hydroxylamines, including unprotected peptide substrates, is described.

(1)H, (13)C, (19)F and (11)B NMR spectral reference data of some potassium organotrifluoroborates

Complete (1)H, (13)C, (19)F and (11)B NMR spectral data for 28 potassium organotrifluoroborates are described. The resonance for the carbon bearing the boron atom is described for most of the studied compounds. A modified (11)B NMR pulse sequence was used and better resolution was observed allowing the observation of (11)B-(19)F coupling constants for some of the studied compounds.

Cobalt(I)-Mediated Preparation of Polyborylated Cyclohexadienes: Scope, Limitations, and Mechanistic Insight

A series of 1,3- and 1,4-diboryl-1,3-cyclohexadienes have been prepared by intermolecular CoCp-mediated [2+2+2] cocyclizations of alkynylboronic pinacolate esters with alkenes, followed by oxidative demetallation with iron(III) chloride. The effect of substitution at the borylated alkyne on chemo- and regioselectivities has been studied, suggesting steric control. The proper choice of substituents allowed the preparation of 1,3-diborylated cyclohexadienes in a highly selective manner. Alternatively, 1,4-diborylated cyclohexadienes could be prepared from diborylated diynes. The scope of this reaction has been examined and found to include electron-poor, electron-rich, linear, and cyclic alkenes. The diborylated cyclohexadienes were submitted to single or double Suzuki-Miyaura cross-coupling reactions with haloarenes to afford polyarylated systems. The mechanism of the title reaction, including the regioselectivity of the cycloaddition steps, has been analyzed by means of DFT computations.

Synthesis of Bicyclic p-Diiodobenzenes via Silver-Catalyzed Csp-H Iodination and Ruthenium-Catalyzed Cycloaddition

Highly substituted iodobenzenes were efficiently and regioselectively synthesized from readily available 1,6-diynes via two-step process consisting of silver-catalyzed Csp-H iodination and subsequent ruthenium-catalyzed [2 + 2 + 2] cycloaddition of resultant iododiynes. Some of the obtained iodobenzenes were subjected to palladium-catalyzed C-C bond-forming reactions such as Mizoroki-Heck reaction, Sonogashira reaction, and Suzuki-Miyaura coupling, giving highly conjugated molecules.