19943-14-7Relevant articles and documents
The Preparation and Resolution of Novel Axially Chiral Pyrazine-Containing P,N Ligands for Asymmetric Catalysis and Their Application in Palladium-Catalysed Allylic Substitution
Goddard, Richard,Guiry, Patrick J.,Kelly, Sarah
, (2022/01/04)
The design and synthesis of two novel pyrazine-containing ligands, 3,6-diisopropyl-Pyrazinap and Np?Cy-Pyrazinap, has been described. Their synthesis was accomplished in six and nine steps, respectively, in which the key steps were the formation of the biaryl linkage through a Suzuki cross-coupling reaction and the formation of the aryl to phosphorus bond employing nickel catalysis. Both ligands were resolved through the formation of diastereomeric palladacycles and in the case of the isolated diastereomer formed from 3,6-diisopropyl-Pyrazinap, an X-ray crystal structure showed the axial chirality to possess (S)-configuration. The two enantiopure ligands were applied to the palladium-catalysed allylic alkylation of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate and afforded conversions of up to 100 % and 99 % with enantioselectivities of up to 92 % ee and 78 % ee, respectively. A series of 1,1,3-triphenylallyl and 1,3-diphenylallyl palladium complexes were prepared and their solution structures and dynamic behaviour elucidated by 2D-COSY and NOESY NMR spectroscopic experiments.
Cyclic dipeptides: Catalyst/promoter-free, rapid and environmentally benign cyclization of free amino acids
Nonappa,Ahonen, Kari,Lahtinen, Manu,Kolehmainen, Erkki
supporting information; experimental part, p. 1203 - 1209 (2011/06/26)
"The best catalyst is no catalyst." With growing public concern over global warming and the amount of greenhouse gases, it is important to reduce the amount of chemicals and eliminate waste, to obtain better results in a simple, selective, safe, and environmentally benign fashion compared to conventional tedious chemical synthesis. Herein, we disclose an environmentally benign, rapid, catalyst/promoter/coupling reagent-free cyclization procedure of free amino acids to furnish exclusively cyclic dipeptides (2,5- diketopiperazines, DKPs) in excellent or even quantitative yield, along with their solid state self-assembling properties. This process is extremely simple and highly efficient with little or no traditional synthetic skills and without any chromatographic purification. Synthesis of structurally diverse DKPs has been achieved with a dramatic decrease in the reaction time, the amount/number of solvents used, a significant increase in the yield and nearly complete elimination of waste. As a result, this is an excellent example for the environmentally benign, clean and green chemistry concept. The most exciting outcome of our investigation is an unusual case of chiral self-recognition encountered upon the cyclization of rac-pipecolic acid, which resulted in the formation of the meso-product exclusively.
Syntheses and properties of zinc and calcium complexes of valinate and isovalinate: Metal α-amino acidates as possible constituents of the early Earth's chemical inventory
Strasdeit, Henry,Buesching, Insa,Behrends, Sabine,Saak, Wolfgang,Barklage, Walter
, p. 1133 - 1142 (2007/10/03)
We have studied the ligand behavior of racemic isovalinate (iva-) and valinate (val-) towards zinc(II) and calcium(II). The following solid metal amino acidates were obtained from aqueous solutions: Zn3Cl2(iva)4 (1). Zn3Cl2(val)4 (2), Zn(val)2 (3). Zn(iva)2 2H2O (4). Zn(iva)2 3.25H2O (5). Zn-(iva)2 (6), Ca(iva)2 x H2O (7), and Ca-(val)2 H2O (8). Except for complex 3, these were hitherto unknown compounds. The conditions under which they formed, together with current ideas of the conditions on early Earth, support the assumption that α-amino acidate complexes of zinc and calcium might have belonged to early Earth's prebiotic chemical inventory. The zinc isovalinates 1. 4. and 5 were characterized by X-ray crystal structure analyses. Complex 1 forms a layer structure containing four- and five-coordinate metal atoms, whereas the zinc atoms in 4 and 5 are five-coordinate. Compound 5 possesses an unprecedented nonpolymeric structure built from cyclic [Zn6(iva)12] complexes, which are separated by water molecules. The thermolyses of solids 1, 3, and 8 at 320°C in an N2 atmosphere yielded numerous organic products, including the cyclic dipeptide of valine from 3 and 8. Condensation, C-C bond breaking and bond formation, aromatization, decarboxylation, and deamination reactions occurred during the thermolyses. Such reactions of metal-bound α-amino acidates that are abiotically formed could already have contributed to an organic-geochemical diversity before life appeared on Earth.
