CAAC Boranes. Synthesis and characterization of cyclic (alkyl) (amino) carbene borane complexes from BF₃ and BH₃

• Julien Monot,
• Louis Fensterbank,
• Max Malacria,
• Emmanuel Lacôte,
• Steven J. Geib and
• Dennis P. Curran

Beilstein J. Org. Chem. 2010, 6, 709–712, doi:10.3762/bjoc.6.82

• carbenes; stable carbenes; Introduction Lewis acid/Lewis base complexes of N-heterocyclic carbenes and boranes (NHC–boranes) are readily prepared from NHC’s and boranes by direct complexation [1][2][3][4]. Unlike many other classes of Lewis base complexes of boranes with neutral molecules (ethers

• , sulfides, etc.), NHC–borane complexes are highly stable in diverse environments. Complexes such as those shown in Figure 1 are white solids that can often be chromatographed if desired. Many such complexes resist decomplexation, oxidation, and both acidic and basic hydrolysis. Such NHC–boranes are

• shown in Figure 3. Of special interest are the lengths of the Ccarbene–N bonds. At 1.294(3) Å for 3a and 1.293(3) Å for 3b, these bonds are significantly shorter than analogous bonds on other NHC–BF3 complexes where the carbene carbon has two nitrogen substituents (1.338(5)–1.355(5) Å) [24][25]. Instead

Suzuki–Miyaura cross-coupling reaction of 1-aryltriazenes with arylboronic acids catalyzed by a recyclable polymer-supported N-heterocyclic carbene–palladium complex catalyst

• Guangming Nan,
• Fang Ren and
• Meiming Luo

Beilstein J. Org. Chem. 2010, 6, No. 70, doi:10.3762/bjoc.6.70

• Suzuki–Miyaura cross-coupling reaction of 1-aryltriazenes with arylboronic acids catalyzed by a recyclable polymer-supported Pd–NHC complex catalyst has been realized for the first time. The polymer-supported catalyst can be re-used several times still retaining high activity for this transformation

• general study on the Suzuki–Miyaura reactions of 1-aryltriazenes under heterogeneous catalysis described to date. Previously, we reported an active and recyclable polystyrene-supported Pd–NHC (N-heterocyclic carbene) catalyst 1 (Scheme 1) for the Suzuki–Miyaura cross-coupling reactions of aryl bromides

• arylboronic acids can be readily effected with our polystyrene-supported Pd–NHC catalyst, which shows high efficiency and can be easily recovered and reused several times still retaining high activity. Results and Discussion The polystyrene-supported Pd–NHC catalyst 1 was prepared according to our reported

The C–F bond as a conformational tool in organic and biological chemistry

• Luke Hunter

Beilstein J. Org. Chem. 2010, 6, No. 38, doi:10.3762/bjoc.6.38

• . The asymmetric transannular aldol reaction catalysed by trans-4-fluoroproline (41), and its application to the total synthesis of (+)-hirsutene (46). The asymmetric Stetter reaction catalysed by chiral NHC catalysts 49–52. The ring conformations of 50–52 are influenced by σCH→σ*CF hyperconjugation. Cy

Synthesis of new C^α-tetrasubstituted α-amino acids

• Andreas A. Grauer and
• Burkhard König

Beilstein J. Org. Chem. 2009, 5, No. 5, doi:10.3762/bjoc.5.5

• (+, 3 C, t-Bu-CH3); 28.4 (+, 3 C, t-Bu-CH3); 32.6 (−, 1 C, CH2); 66.5 (−, 0.1 C, cis-OCH2); 66.6 (−, 0.9 C, trans-OCH2); 67.6 (Cquat, 1 C, NHC); 82.3 (Cquat, 2 C, t-Bu-C); 87.5 (+, 1 C, CH); 154.0 (Cquat, 0.1 C, cis-NHCO); 154.4 (Cquat, 0.9 C, trans-NHCO); 171.2 (Cquat, 0.1 C, cis-COO); 171.3 (Cquat

• -NHC); 68.2 (Cquat, 0.8 C, trans-NHC); 79.8 (Cquat, 1 C, t-Bu-C); 81.7 (Cquat, 0.2 C, cis- t-Bu-C); 82.0 (Cquat, 0.8 C, trans- t-Bu-C); 82.1 (+, 0.8 C, trans-CH); 82.8 (+, 0.2 C, cis-CH); 154.7 (Cquat, 0.8 C, trans-NHCO); 155.1 (Cquat, 0.2 C, cis-NHCO); 170.6 (Cquat, 0.2 C, cis-COO); 170.7 (Cquat, 0.8

• , 0.25 C, cis-NHC); 68.2 (Cquat, 0.75 C, trans-NHC); 79.8 (Cquat, 1 C, t-Bu-C); 81.7 (Cquat, 0.25 C, cis- t-Bu-C); 82.0 (Cquat, 0.75 C, trans- t-Bu-C); 84.1 (+, 0.75 C, trans-CH); 84.5 (+, 0.25 C, cis-CH); 154.8 (Cquat, 0.25 C, cis-NHCO); 155.1 (Cquat, 0.75 C, trans-NHCO); 170.6 (Cquat, 0.75 C, trans-COO

Expedient syntheses of the N-heterocyclic carbene precursor imidazolium salts IPr·HCl, IMes·HCl and IXy·HCl

• Lukas Hintermann

Beilstein J. Org. Chem. 2007, 3, No. 22, doi:10.1186/1860-5397-3-22

• -dimethylphenyl), precursors to widely used N-heterocyclic carbene (NHC) ligands and catalysts, were prepared in high yields (81%, 69% and 89%, respectively) by the reaction of 1,4-diaryl-1, 4-diazabutadienes, paraformaldehyde and chlorotrimethylsilane in dilute ethyl acetate solution. A reaction mechanism

• prominent members of the family of N-heterocyclic carbenes (NHC) are the sterically encumbered imidazolylidenes IPr and IMes (Figure 1), which can also be considered as analogues of bulky and electron-rich tertiary phosphanes. In contrast to the latter, their synthesis does not involve air-sensitive or