109651-07-2Relevant articles and documents
Transition Metal-Catalysed Intramolecular Carbenoid C?H Insertion for Pyrrolidine Formation by Decomposition of α-Diazoesters
Solé, Daniel,Amenta, Arianna,Mariani, Francesco,Bennasar, M.-Llu?sa,Fernández, Israel
, p. 3654 - 3664 (2017/09/13)
The use of Pd-, Rh(II)- and Ru(II)-based catalysts has been explored in the transition metal-catalysed intramolecular carbenoid C?H insertion of α-diazoesters leading to pyrrolidines. Although the outcome of the reaction was highly substrate-dependent, in general, it was possible to control the chemoselectivity of the process towards pyrrolidines by adequate catalyst selection. The Pd(0)-catalysts were as efficient as [Rh(Ph3CCO2)2]2 in promoting the C(sp3)?H insertion of ortho-substituted anilines. In contrast, for anilines bearing meta- and para-substituents, the Rh(II)-catalyst provided the best chemoselectivities and reaction yields. On the other hand, [Ru(p-cymene)Cl2]2 was the most efficient catalyst for the insertion reaction of the N-benzyl-N-phenyl and N,N-dibenzyl α-diazoesters, while the C(sp3)?H insertion of the N-benzylsulfonamide substrate was only promoted by [Rh(Ph3CCO2)2]2. According to density functional theory (DFT) calculations, the mechanism involved in the Pd(0)- and Ru(II)-catalysed C(sp3)?H insertions differs considerably from that typically proposed for the Rh(II)-catalysed transformation. Whereas the Pd(0)-catalysed reaction involves a Pd-mediated 1,5-H migration from the C(sp3)?H bond to the carbenoid carbon atom leading to the formal oxidation of the transition metal, a Ru(II)-promoted Mannich type reaction involving a zwitterionic intermediate seems to be operative in the Ru(II)-catalysed transformation. (Figure presented.).
Stereoselective synthesis and conformational analysis of unnatural tetrapeptides. Part 2
Almiento, Giosue M.,Balducci, Daniele,Bottoni, Andrea,Calvaresi, Matteo,Porzi, Gianni
, p. 2695 - 2711 (2008/09/17)
Stereoselective synthesis of unnatural tetrapeptides 20a and 20b, 21a and 21b and 30 and 31, containing two l-valine units and two unnatural α-amino acids (ornithine and modified aspartic acid), has been accomplished starting from the l-valine derived chiral synthon 1. Structural investigations of these non-proteinogenic peptides have been carried out on the acetamido derivatives using 1H NMR, IR spectroscopic techniques and a conformational analysis based on molecular dynamics (MD) and cluster analysis.
