N-Trityl-aziridinyl alcohols as highly efficient chiral catalysts in asymmetric additions of organozinc species to aldehydes

A synthetic route leading to a series of new chiral catalysts containing the N-trityl-aziridine moiety and a primary and a secondary hydroxyl group as nucleophilic centers is described. All the new compounds have been tested as chiral catalysts in the enantioselective addition of diethylzinc and phenylethynylzinc to aryl and alkyl aldehydes, yielding the corresponding chiral alcohols in high chemical yields (up to 96%) and with excellent ee’s of ca. 90%. The influence of the stereogenic centers located at the carbon atom bonded with the hydroxyl moiety and on the carbon of the aziridine ring on the stereochemistry of the addition reactions is also discussed.

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(S)-(−)-1-Triphenylmethyl-2-α-hydroxyethylaziridineC23H23NOEe = 99%[α]20D = −2.7 (c 1, CHCl3) (measured for the 59:41 mixture of diastereoisomers)Source of chirality: asymmetric synthesisAbsolute configuration: (S) for aziridine (literature data), nd for C-OH

(S)-(−)-1-Triphenylmethyl-2-α-hydroxybenzylaziridineC28H25NOEe = 98%[α]20D = −2.9 (c 1, CHCl3) (measured for the 59:41 mixture of diastereoisomers)Source of chirality: asymmetric synthesisAbsolute configuration: (S) for aziridine (literature data), nd for C–OH

(S)-(−)-1-Triphenylmethyl-2-α-hydroxy-3-methylpropylaziridineC25H27NOEe = 99%[α]20D = −2.5 (c 1, CHCl3) (measured for the 59:41 mixture of diastereoisomers)Source of chirality: asymmetric synthesisAbsolute configuration: (S) for aziridine (literature data), nd for C–OH

(R)-(+)-1-Triphenylmethyl-2-α-hydroxyethylphenylaziridineC29H27NOEe = 98%[α]20D = +5.0 (c 1, CHCl3) (measured for the 59:41 mixture of diastereoisomers)Source of chirality: asymmetric synthesisAbsolute configuration: (R) for aziridine (literature data), nd for C–OH