Tropos Amino Alcohol Mediated Enantioselective Aryl Transfer Reactions to Aromatic Aldehydes

Abstract

Keywords: Asymmetric catalysis / Ligand design / Enantioselectivity / Atropisomerism / Amino alcoholsThe preparation of new chiral amino alcohols that possess a flexible biphenylazepine moiety and can work as tropos catalysts, is presented. In these compounds, the sign of the induced axial chirality depends on the nature of stereogenic centers near the flexible fragment and can determine the stereochemical outcome in asymmetric reactions mediated by them. The efficiency of these new ligands has been ex- [a] 5939 plored in the asymmetric addition of arylzinc species prepared in situ to aromatic aldehydes. Among them, amino alcohol (1R,2S)-4 gave the best results and afforded optically active diarymethanols, which are precursors of well-known chiral drugs, in high yields and with enantioselectivity up to 96 %.www.eurjoc.org

Absolute Configuration Assignment to Chiral Natural Products by Biphenyl Chiroptical Probes: The Case of the Phytotoxins Colletochlorin A and Agropyrenol

“…Some years ago we introduced the use of the 2,2′-bridged biphenyl chiroptical probes, which proved to be versatile, reliable, and efficient tools for AC assignment to chiral diols, 23 carboxylic acids, 24 and primary amines. 25 In these systems, due to the low aryl–aryl rotational barrier displayed by the biphenyl moiety, 26 a central-to-axial chirality induction occurs between the chiral substrate and the biphenyl itself which, in turn, assumes a preferred M or P twist depending on the AC of the substrate. Moreover, the sense of the biphenyl twist is readily revealed by the sign of the ECD Cotton effect at 250 nm, in correspondence to the biphenyl A band absorption.…”

Amino alcohol‐derived chiral stationary phases

“…However, the chiral amino alcohols are readily available on their own, and many amino alcohols cannot be prepared from the amino acids; thus, the starting materials are classified separately from the amino acids. Amino alcohols are examples of the simple chiral compounds that have been widely used in various fields 41–89 . They have been used as starting materials to prepare the chiral catalysts used in the asymmetric organic synthesis and to prepare chiral NMR chemical shift reagents 41–63 …”

“…Amino alcohols are examples of the simple chiral compounds that have been widely used in various fields 41–89 . They have been used as starting materials to prepare the chiral catalysts used in the asymmetric organic synthesis and to prepare chiral NMR chemical shift reagents 41–63 …”

5,5,7,7-Tetrametyl-6,7-dihydro-5H-dibenzo[c,e]azepine

“…Dibenz[c,e]azepines constitute an important class of compounds widely employed as chiral or pro-chiral scaffolds for the construction of chiral catalysts for asymmetric synthesis or probes for chiral molecular recognition. In particular, 1,1 -binaphthylazepines have been widely employed as chiral ligands in organometallic catalysis [1][2][3][4][5] and organocatalysis [6][7][8][9][10], while not-atropisomerically stable (i.e., tropos) 1,1 -biphenylazepines have been reported both as structural motifs for the construction of the chiral ligands [9][10][11][12][13][14][15] and as the chiroptical probes for the absolute configuration assignment to the chiral acids [16][17][18][19] and amines [14,20]. In fact, in 1,1 -biphenylazepines the low phenyl-phenyl rotational barrier allows, at room temperature, a free interconversion of the two possible M and P atropisomeric forms.…”