204917-65-7Relevant academic research and scientific papers
Mechanistic Evaluation of the Halocyclization of 4-Penten-1-ol by Some Bis(2-substituted pyridine) and Bis(2,6-disubstituted pyridine)bromonium Triflates
Cui, Xi-Lin,Brown
, p. 5653 - 5658 (2000)
The halocyclization reaction of 4-penten-1-ol mediated by various bis(2-substituted pyridine) and (2,6- disubstituted pyridine)bromonium triflates (P2Br+OTf-) was investigated to determine the influence of the substituents on the mechanism of reaction. In all cases, the reaction proceeds via a two-step process where the starting P2Br+ reversibly dissociates to a reactive monosubstituted PBr+, which then is captured by 4-penten-1-ol to form halocyclized product (2-bromomethyltet-rahydrofuran). The dissociation rate constant of P2Br+ (kd) is sensitive to the steric bulk at the 2- and 6-positions, and in the case of the 2,6-dicyclohexylpyridine or 2,6-dicyclopentylpyridine, the P2Br+ species are too unstable to isolate. The partitioning ratio of the reactive intermediate (PBr+) between reversal and product formation (k-d/k2) is not particularly sensitive to the nature of the pyridine, the limiting values being 3-7 except in the case of bis(2(-)-menthylpyridine)bromonium triflate where the k-d/k2 ratio is ～80. The reaction of 4-penten-1-ol and its OD isotopomer with bis(lutidine)bromonium triflate was investigated to determine the deuterium kinetic isotope effect (dkie) on the bromocyclization reaction. The (k-d/k2)H/D ratio is 1.0, indicating that the rate-limiting step for the bromocyclization is probably formation of a PBr+-4-penten-1-ol complex which does not involve substantial changes in the bonding of the OH. The cyclization of 4-penten-1-ol and 4-pentenoic acid mediated by bis(2(-)-menthylpyridine)bromonium triflate produces an enantiomeric excess in the cyclized products of only 2.4% and 4.8% respectively.
Enantioselective catalysis. Part 119: New chiral 2-(2- pyridinyl)oxazoline ligands containing an additional optically active substituent in the pyridine system
Brunner, Henri,Stoeriko, Reinhard,Nuber, Bernhard
, p. 407 - 422 (2007/10/03)
The synthesis of novel chiral nitrogen ligands and their precursors is described. They consist of an optically active oxazoline bound to pyridine in the 2-position. In addition, another optically active substituent is attached to the pyridine ring. The effect of the two independent stereogenic units in one ligand was studied in the Rh(I)catalysed enantioselective hydrosilylation of acetophenone with diphenylsilane.
