Synthesis of new chiral hydroxy oxazolines and their use in the catalytic asymmetric phenyl transfer to aldehydes
摘要:
Starting either from benzoylformic acid or ethyl oxamate and enantiopure beta-amino alcohols, several chiral alpha-hydroxy oxazolines have been prepared by short synthetic routes. Subsequently, they have been employed in the catalytic asymmetric phenyl transfer to various aldehydes, using a mixture of triphenylborane and diethylzinc as the phenyl source. The corresponding secondary alcohols were obtained with good enantioselectivities (up to 81% ee) and up to 92% yield. (c) 2005 Elsevier Ltd. All rights reserved.
Highly Enantio- and Regioselective Allylic Alkylations Catalyzed by Chiral [Bis(dihydrooxazole)]molybdenum Complexes
摘要:
A series of chiral C-2-symmetric bis[dihydrooxazoles] with a trans-1,2-diaminocyclohexane backbone was synthesized. In view of the promising results obtained by Trost et al with related bis[pyridine] ligands, we tested these new ligands in the enantioselective molybdenum-catalyzed allylic alkylation of 1- and 3-monosubstituted allylic substrates. Enantiomer excesses of up to 98% and branched/linear ratios of up to 11 : 1 were obtained with (E)-3-(alkyl)allyl carbonates. (E)-3-Phenoxyallyl acetate gave a branclied/linear ratio of > 20:1 and an ee of 98%. Crystal structures of the free ligand 7a and of its tricarbonylmolybdenum(0) complex 28 are reported.