title: Absolute asymmetric synthesis of "chiral-at-metal" Grignard reagents and transfer of the chirality to carbon.
abstract: Two new six-coordinate Grignard reagents, cis-[(p-CH(3)C(6)H(4))MgBr(dme)(2)] (1) and cis-[MgCH(3)(thf)(dme)(2)]I (2), have been synthesized and their crystal structures have been determined. Both reagents are cis-octahedral and therefore chiral. They crystallize as conglomerates and racemize rapidly in solution. By utilizing these properties, the absolute asymmetric synthesis of specifically the Delta or the Lambda enantiomer was achieved for both Grignard reagents. Enantiopure 1 and 2 were then reacted with butyraldehyde or benzaldehyde to give the corresponding alcohol in up to 22 % enantiomeric excess. At -60 degrees C, the Grignard reagents crystallize as racemic phases instead of conglomerates. Consequently, the crystal structures of rac-cis-[(p-CH(3)C(6)H(4))MgBr(dme)(2)].DME (3) and rac-cis-[MgCH(3)(thf)(dme)(2)]I (4) could be determined.
authors.affiliation: Organic Chemistry, Department of Chemistry, Göteborg University, 412 96 Göteborg, Sweden.
authors.forename: Marcus
authors.initials: M
authors.lastname: Vestergren
authors.forename: Johan
authors.initials: J
authors.lastname: Eriksson
authors.forename: Mikael
authors.initials: M
authors.lastname: Håkansson