Mandelic acid derived α-aziridinyl alcohols as highly efficient ligands for asymmetric additions of zinc organyls to aldehydes

A straightforward synthesis of a series of new catalysts containing secondary hydroxyl and aziridine moieties as nucleophilic centers built on the chiral scaffold of (S)-(+)-mandelic acid is described. The new compounds have been tested for the enantioselective addition of diethylzinc and phenylethynylzinc to aryl and alkyl aldehydes, which yielded the corresponding chiral alcohols in high chemical yields (up to 95%) and with excellent ee’s of ca. 90%. The strong influence of the stereogenic center located at the aziridine subunit on the stereochemical outcome is also reported on.

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(S)-(+)-2-((R)-2-Methylaziridin-1-yl)-1-phenylethanolC11H16NOee = 99%[α]Drt=+30.0 (c 1, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (S,R) (literature data)

(S)-(+)-2-(2,2-Dimethylaziridin-1-yl)-1-phenylethanolC12H18NOee = 98%[α]Drt=+8.6 (c 1, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (S) (literature data)

(S)-(−)-2-((R)-2-Isopropylaziridin-1-yl)-1-phenylethanolC13H20NOe = 99%[α]Drt=-47.7 (c 1, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (S,R) (literature data)

(S)-(+)-2-((S)-2-Isopropylaziridin-1-yl)-1-phenylethanolC13H20NOee = 98%[α]Drt=+3.0 (c 1, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (S,S) (literature data)