188762-02-9Relevant academic research and scientific papers
Asymmetric reduction of ketones with catecholborane using 2,6-Bodol complexes of titanium(IV) as catalysts
Sarvary, Ian,Almqvist, Fredrik,Frejd, Torbjoern
, p. 2158 - 2166 (2001)
Reductions performed with TiIV complexes of ligands based on bicyclo[2.2.2]octane diols 5 and 6 are effective catalysts in the reduction of prochiral ketones to optically active alcohols, with catecholborane as the reducing agent. Methyl ketones are favored and enantiomeric excesses (ee) of ≤98% have been achieved with acetophenone as the substrate. Several other substrates were tested, among them 2-octanone, which gave 2-octanol in 87 % ee. Further details of the method were examined, for example, temperature, solvent composition, amount of molecular sieves (4 A), and catecholborane quality, as well as the sensitivity of the ligands towards acids. NMR spectroscopic methods were used to gain some insight into the complexes formed between the ligands and [Ti(OiPr)4]. A dimeric structure is proposed for the pre-catalyst.
Bicyclo[2.2.2]octane-derived chiral ligands-synthesis and application of BODOLs in the asymmetric reduction of acetophenone with catecholborane
Friberg, Annika,Sarvary, Ian,Wendt, Ola F.,Frejd, Torbjoern
, p. 1765 - 1777 (2008/12/23)
An improved synthetic route to the bicyclo[2.2.2]octane-2,6-diol ligands (2,6-BODOLs) allowed an increased structural variation of the ligand side-arm. The addition of aromatic or vinylic Grignard reagents to hydroxyketone 1 was highly selective and ligands 3f-3l were isolated in 84-97% yield. The addition of alkyl Grignard reagents containing β-hydrogens resulted in lower yields (13-71%) due to competing ketone reduction. A number of 2,5-BODOLs were synthesized using a similar methodology. The ligands, together with Ti(OiPr)4, were tested in the asymmetric reduction of acetophenone with catecholborane (up to 98% ee). 1-Naphthyl-BODOL 3i was employed as an allylboration reagent to benzaldehyde together with Sc(OTf)3, resulting in (1S)-1-phenyl-3-buten-1-ol in 80% ee.
New ligands for the titanium(IV)-induced asymmetric reduction of ketones with catecholborane
Almqvist,Torstensson,Gudmundsson,Frejd
, p. 376 - 377 (2007/10/03)
High to moderate enantiomeric excesses were achieved for the reduction of ketones with catecholborane in the presence of a titanium-based catalyst bearing the new optically active diols 1 a or 1 b as ligands. Of particular interest is the relatively high enantiomeric excess obtained in the reductions of linear nonaromatic methyl ketones.
