Synthesis and structure of trans-bis(1,4-dimesityl-3-methyl-1,2,3-triazol-5-ylidene)palladium(II) dichloride and diacetate. Suzuki–Miyaura coupling of polybromoarenes with high catalytic turnover efficiencies

• Jeelani Basha Shaik,
• Venkatachalam Ramkumar,
• Babu Varghese and
• Sethuraman Sankararaman

Beilstein J. Org. Chem. 2013, 9, 698–704, doi:10.3762/bjoc.9.79

• -dimesityl-3-methyl-1,2,3-triazolium iodide with freshly prepared silver oxide followed by transmetalation with Pd(Cl)2(CH3CN)2 yielded 1 as a pale yellow solid in 87% (Scheme 1). The acetate complex 2 was prepared by the transmetalation of the silver carbene complex with Pd(OAc)2. Addition of Pd(OAc)2 to in

• electronics applications. Experimental 1,4-Dimesityl-3-methyl-1,2,3-triazolium iodide was prepared from the corresponding triazole, which in turn was prepared by the click reaction of mesitylacetylene and mesitylazide according to the literature [27]. Complex 1 was synthesized in a similar manner as reported

• previously [27]. Synthesis of complex 1 [27] 1,4-Dimesityl-3-methyl-1,2,3-triazolium iodide (250 mg, 0.56 mmol) was treated with freshly prepared silver oxide (78 mg, 0.34 mmol, 0.6 equiv) in CH2Cl2 (12 mL). The solution was stirred at room temperature in the dark for 8 h. The silver carbene complex thus

Chemoenzymatic synthesis and biological evaluation of enantiomerically enriched 1-(β-hydroxypropyl)imidazolium- and triazolium-based ionic liquids

• Paweł Borowiecki,
• Małgorzata Milner-Krawczyk and
• Jan Plenkiewicz

Beilstein J. Org. Chem. 2013, 9, 516–525, doi:10.3762/bjoc.9.56

• (+)-8a–c and (+)-8e–f, which are exceedingly viscous liquids (gums), all of the chiral hydroxy-functionalized imidazolium and one of the triazolium salts are liquid at room temperature. Final products were characterized by 1H, 13C NMR and FTIR spectroscopy as well as high-resolution electrospray

• 5). Moreover, the chemical nature of the cationic head group influenced the overall toxicity of the CILs, which is in good agreement with several previous studies [60]. The imidazolium CILs exhibited visibly stronger antibacterial and antifungal activity than triazolium CILs (Tables 4–6). However

• compounds exhibited biological activity that was significantly dependent on the alkyl chain length, with considerably high toxicity of the substituents with 10–16 carbon atoms. The imidazolium salts revealed stronger antibacterial activity than their triazolium analogues. Model for the configurational

N-Heterocyclic carbene-catalyzed direct cross-aza-benzoin reaction: Efficient synthesis of α-amino-β-keto esters

• Takuya Uno,
• Yusuke Kobayashi and
• Yoshiji Takemoto

Beilstein J. Org. Chem. 2012, 8, 1499–1504, doi:10.3762/bjoc.8.169

• -coupling of 1a was obtained. Encouraged by this result, we then attempted the other precatalysts 3b–e depicted in Figure 2. Imidazolium salt 3b and simple triazolium salt 3c gave no coupled product 5a (Table 1, entries 2 and 3). Further screening revealed that bicyclic triazolium salt 3d could catalyze the

• the cross-aza-benzoin reaction is shown in Scheme 3. Carbene I is generated by deprotonation of triazolium salt 3e in the presence of K2CO3. The carbene I reacts with aldehyde 1 to afford Breslow intermediate II, which could lead to benzoin (6), or tetrahedral intermediate III when treated with α

A quantitative approach to nucleophilic organocatalysis

• Herbert Mayr,
• Sami Lakhdar,
• Biplab Maji and
• Armin R. Ofial

Beilstein J. Org. Chem. 2012, 8, 1458–1478, doi:10.3762/bjoc.8.166

• -unsaturated aldehydes can thus be explained by the low acidity of imidazolium ions [59]. Unlike triazolium and tetrazolium ions, imidazolium ions are unable to transfer a proton to the enamine unit in 16 (corresponding to 5 in the general Figure 2), which is necessary to close the catalytic cycle shown in

N-Heterocyclic carbene/Brønsted acid cooperative catalysis as a powerful tool in organic synthesis

• Rob De Vreese and
• Matthias D’hooghe

Beilstein J. Org. Chem. 2012, 8, 398–402, doi:10.3762/bjoc.8.43

• ” reactions of aldehydes started as long ago as 1832, and the preparation of sterically hindered triazolium salts in 1996 provided a solid basis for highly stereoselective “umpolung” reactions utilizing NHCs [12]. In addition, conjugate “umpolung” relates to a process in which α,β-unsaturated aldehydes 3 are

• anion 8 can deprotonate pentafluorophenyl triazolium salts 7 to give the free carbenes 5 and acetic acid 6, pointing to the peculiar conclusion that this carboxylic acid does not neutralize the carbenes (Scheme 3) [21]. Probably, the presence of the electron-withdrawing pentafluorophenyl group in

• that the combination of a pentafluorophenyl triazolium carbene 5 and a Brønsted acid with low pKa value may provide new opportunities for the design of reaction pathways in which the carbene and the acid play different roles. The idea to use a very weak base in NHC catalysis has also been described by

A ferrocene redox-active triazolium macrocycle that binds and senses chloride

• Nicholas G. White and
• Paul D. Beer

Beilstein J. Org. Chem. 2012, 8, 246–252, doi:10.3762/bjoc.8.25

• state by X-ray crystallography. Alkylation gives the corresponding triazolium macrocycle, which binds chloride and benzoate strongly in CD3CN solution through favourable charge-assisted C–H···anion interactions, as evidenced by 1H NMR titration experiments. Preliminary electrochemical studies reveal

• that the redox-active macrocycle is capable of sensing chloride in CH3CN solution. Keywords: anion binding; C–H···anion interactions; electrochemistry; ferrocene; triazolium; Introduction The copper(I)-catalysed cycloaddition of alkynes and azides (CuAAC) [1][2] to give the 1,2,3-triazole group is

• ][7]. More recently, we [8], and others [9][10], have shown that alkylating the triazole group to give the triazolium group increases the strength of anion binding significantly by further polarising the C–H bond of the heterocycle. With one notable recent exception of an acyclic ferrocene-appended