Enantioselective reduction of prochiral ketones by catecholborane catalysed by chiral group 13 complexes
LiGaH4, in combination with the S,O-chelate 2-hydroxy-2'-mercapto-1,1'-binaphthyl (MTBH2), forms an active catalyst for the asymmetric reduction of prochiral ketones, with catecholborane as the hydride source. Enantioface differentiation is on the basis of the steric requirements of the ketone substituents. Aryl/ n-alkyl ketones are reduced in 90-93% ee and RC(O)Me (e.g. R = iPr, cycloC6H11, tBu) in 60-72% ee. Other borane sources and alternative catalyst structures based on indium do not form enantioselective catalysts.
Blake
AJ
School of Chemistry, The University of Nottingham, University Park, UK. a.j.blake@nottingham.ac.uk
Cunningham
A
Ford
A
Teat
SJ
Woodward
S