229326-81-2Relevant articles and documents
Highly Efficient Synthesis of Enantiomerically Pure (S)-2-Amino-1,2,2-triphenylethanol. Development of a New Family of Ligands for the Highly Enantioselective Catalytic Ethylation of Aldehydes
Reddy, Katamreddy Subba,Sola, Lluis,Moyano, Albert,Pericas, Miquel A.,Riera, Antoni
, p. 3969 - 3974 (2007/10/03)
The reaction of (S)-triphenylethylene oxide (3) with diisopropoxytitanium(IV) diazide in benzene solution at 70°C takes place readily in a completely regioselective and stereospecific manner to afford (S)-2-azido-1,2,2-triphenylethanol (6). Reduction of the azide by catalytic hydrogenation leads to (S)-2-amino-1,2,2-triphenylethanol (5) that, by N,N-dialkylation with 1,4-dibromobutane, 1,5-dibromopentane, 1,5-dibromo-3-oxapentane, α,α′-dibromo-o-xylene, and methyl iodide, affords the corresponding (S)-2-dialkylamino-1,2,2-triphenylethanols (7a-e). On the other hand, the reaction of 5 with benzyl bromide or 1-iodobutane takes place as a monoalkylation, leading to the corresponding (S)-2-alkylamino-1,2,2-triphenylethanols (8f,g). The performance of amino alcohols 7a-e as ligands for the catalytic enantioselective addition of diethylzinc to benzaldehyde has been studied, with enantioselectivities of 94-97% being recorded. The best performing ligands in this family, 7a [(S)-1,2,2-triphenyl-2-(1-pyrrolidinyl)-ethanol] and 7c [(S)-2-morpholino-1,2,2-triphenylethanol] have been studied in the addition of Et2Zn to a representative family of aldehydes. With 7a, a 96.6% mean ee is recorded for a family of 16 α-substituted aldehydes and a 92.8% mean ee for a family of six α-unsubstituted aldehydes. With 7c working on the same families of aldehydes, the mean enantioselectivities are 96.8% and 91.8%, respectively.
