Zinc(II) mediated asymmetric aldol condensation catalyzed by chiral aziridine ligands

Highly enantioselective asymmetric direct aldol reaction promoted by aziridine amides constructed on chiral terpene scaffold

“…In continuation of our research, we decided to examine the catalytic activity of the newly obtained terpene‐based aziridine amides. All the desired ligands were tested in asymmetric aldol reaction of acetone with 4‐nitrobenzaldehyde in the presence of 5 mol% of catalyst and 5 mol% of Zn(OTf) 2 in acetone/water (1.8/0.2) mixture (Scheme , Table ), as described in our earlier work …”

“…All the desired ligands were tested in asymmetric aldol reaction of acetone with 4-nitrobenzaldehyde in the presence of 5 mol% of catalyst and 5 mol% of Zn(OTf) 2 in acetone/water (1.8/0.2) mixture (Scheme 2, Table 2), as described in our earlier work. 30,31 Screening of the ligands showed that, besides the terpene subunit, ligands bearing an achiral 2,2′-dimethylaziridine subunit (2a, 4a, 6a) have very limited use in leading to the aldol adducts in low chemical yields (3-16%) and without any enantioselectivity. The use of ligands with chiral aziridine like (S)-2-methylaziridine (2b, 4b, 6b) resulted in increasing the chemical yields even to 96%, but the enantioselectivity was still poor (4-20% of ee).…”

“…On the other hand, previously we reported a zinc(II)‐mediated efficient asymmetric aldol reaction promoted by various chiral catalysts bearing an aziridine moiety . Chiral aziridine ligands have proven also to be efficient in other asymmetric reactions in the presence of zinc ions …”

“…22,23 On the other hand, previously we reported a zinc(II)mediated efficient asymmetric aldol reaction promoted by various chiral catalysts bearing an aziridine moiety. 30,31 Chiral aziridine ligands have proven also to be efficient in other asymmetric reactions in the presence of zinc ions. [32][33][34] On the basis of the aforementioned results and in order to continue our studies on the stereocontrolled reaction of the formation of carbon-carbon bonds, we decided to synthesize a series of optically pure β-hydroxyamides constructed on the chiral scaffold of camphor, fenchone, and menthone in which a ring of chiral aziridine constitutes an amine function of amide.…”

Synthesis of chiral 1-(2-aminoalkyl)aziridines via the self-opening reaction of aziridine

“…At this point it should be mentioned that enantiomerically pure aziridine derivatives (alcohols, semicarbazides, sulfoxides, ethers) strongly coordinate to zinc species, exhibiting excellent catalytic properties in asymmetric reactions performed in the presence of zinc ions, 12 namely the addition of diethylzinc and phenylethynylzinc [16][17][18][19][20] to various carbonyl compounds or in Zn(OTf) 2 -catalyzed aldol condensation. 21,22 The synthetic diversity and broad mode of application of chiral diamines prompted us to explore the synthesis of optically pure aziridine-containing diamines. Our efforts were focused on developing a method of synthesis of optically pure diamines in which the chiral aziridine ring would bear a β-aminoalkyl group on the nitrogen atom.…”