Selective Lithiation of 4-(1H-1-Pyrrolyl)pyridine. Access to New Electron-Releasing Ligands

Synthesis of 2-(2-Pyridyl)-2H-azirines via Metal-Free C-C Cross-Coupling of Bromoazirines with 2-Stannylpyridines

A high-yield method for the introduction of a 2-pyridyl substituent in the C2 position of the three-membered ring of 2-bromo-2H-azirine-2-carboxylic acid derivatives by the direct cross-coupling with 2-(trialkylstannyl)pyridines has been described. The reaction works well with 3-, 4-, or 5-substituted 2-stannylpyridines and can be also employed for the synthesis of 2-(thiazol-2-yl)-2H-azirines. According to DFT calculations, the reaction proceeds through the sequence of S_N2'-substitution of bromine, 1,4-stannyl shift, and [2,3]-sigmatropic shift of the pyridine ring.

The 2-Pyridyl Problem: Challenging Nucleophiles in Cross-Coupling Arylations

Azine-containing biaryls are ubiquitous scaffolds in many areas of chemistry, and efficient methods for their synthesis are continually desired. Pyridine rings are prominent amongst these motifs. Transition-metal-catalysed cross-coupling reactions have been widely used for their synthesis and functionalisation as they often provide a swift and tuneable route to related biaryl scaffolds. However, 2-pyridine organometallics are capricious coupling partners and 2-pyridyl boron reagents in particular are notorious for their instability and poor reactivity in Suzuki-Miyaura cross-coupling reactions. The synthesis of pyridine-containing biaryls is therefore limited, and methods for the formation of unsymmetrical 2,2'-bis-pyridines are scarce. This Review focuses on the methods developed for the challenging coupling of 2-pyridine nucleophiles with (hetero)aryl electrophiles, and ranges from traditional cross-coupling processes to alternative nucleophilic reagents and novel main group approaches.

Building C(sp3 ) Molecular Complexity on 2,2'-Bipyridine and 1,10-Phenanthroline in Rhenium Tricarbonyl Complexes

The reactions of [Re(N-N)(CO)₃ (PMe₃ )]OTf (N-N=2,2'-bipyridine, bipy; 1,10-phenanthroline, phen) compounds with tBuLi and with LiHBEt₃ have been explored. Addition to the N-N chelate took place with different site-selectivity depending on both chelate and nucleophile. Thus, with tBuLi, an unprecedented addition to C5 of bipy, a regiochemistry not accessible for free bipy, was obtained, whereas coordinated phen underwent tBuLi addition to C2 and C4. Remarkably, when LiHBEt₃ reacted with [Re(bipy)(CO)₃ (PMe₃ )]OTf, hydride addition to the 4 and 6 positions of bipy triggered an intermolecular cyclodimerization of two dearomatized pyridyl rings. In contrast, hydride addition to the phen analog resulted in partial reduction of one pyridine ring. The resulting neutral Re^I products showed a varied reactivity with HOTf and with MeOTf to yield cationic complexes. These strategies rendered access to Re^I complexes containing bipy- and phen-derived chelates with several C(sp³ ) centers.

Unusual reactivity patterns of 1,3,6,8-tetraazatricyclo-[4.4.1.1(3,8)]-dodecane (TATD) towards some reducing agents: synthesis of TMEDA

N,N,N,N-tetramethylethylenediamine (TMEDA) can be synthesized by simple reduction of 1,3,6,8-tetraazatricyclo-[4.4.1.1.(3,8)]dodecane (TATD), an aminal cage type amine, with formic acid. The aminal can be converted to TMEDA in high yield very easily and in a very short time. We comment on the scope and limitations of the reduction of this aminal and propose a possible reaction mechanism.

Tuning of Ruthenium Complex Properties Using Pyrrole- and Pyrrolidine-Containing Polypyridine Ligands

The effect of pyrrole- and pyrrolidine-containing ligands (L) on the properties of heteroleptic [RuL2dcbpy]2+ complexes has been investigated. TiO2 electrodes modified with the new complexes exhibited extended absorption domains and high absorbances. Providing that a cobalt-based mediator was used for regeneration of the RuII state, good incident photon-to-current efficiency (near 80%) values were obtained in the pyrrole series.

Pyrrolidine-Containing Polypyridines: New Ligands for Improved Visible Light Absorption by Ruthenium Complexes

[reaction: see text] A range of new electron-releasing pyrrolidine-containing bipyridines and terpyridines has been prepared via selective metalation-cross-coupling sequences. The obtained ligands have been involved in microwave-assisted ruthenium complexation leading to homoleptic complexes in high yield. The electron-donor effect of the pyrrolidine nucleus led to a notable improvement of visible light absorption and strong changes in the electrochemical behavior, opening new opportunities for the design of photovoltaic devices.