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Catalytic Enantioselective Hydrosilylation of Ketones with Rhodium‐Phosphite Complexes Containing a TADDOLate and a Dihydrooxazole Unit
Author(s) -
Heldmann Dieter K.,
Seebach Dieter
Publication year - 1999
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/(sici)1522-2675(19990707)82:7<1096::aid-hlca1096>3.0.co;2-i
Subject(s) - chemistry , enantioselective synthesis , rhodium , medicinal chemistry , ligand (biochemistry) , catalysis , enantiomer , aryl , isopropyl , ring (chemistry) , alkyl , dioxolane , stereochemistry , hydrosilylation , chirality (physics) , organic chemistry , biochemistry , receptor , nambu–jona lasinio model , chiral symmetry breaking , physics , quantum mechanics , quark
New types of chiral phosphorus/nitrogen ligands, capable of forming six‐membered‐ring metal chelates have been prepared from α , α , α ′, α ′‐tetraaryl‐1,2‐dioxolane‐4,5‐dimethanols (TADDOLs), PCl 3 , and dihydrooxazole alcohols (from amino acids) ( 7 in Scheme 1 ). The X‐ray crystal structure of a Rh complex of one of these ligands, 8b , has been determined ( Scheme 2 and Fig. ). Enantioselective hydrosilylations of dialkyl and aryl alkyl ketones with Ph 2 SiH 2 /0.01 equiv. Rh I ⋅ 7 have been studied and found to provide secondary alcohols in enantiomer ratios of up to 97 : 3 ( Scheme 3 and Table ). The ligand prepared from ( R , R )‐TADDOL and the ( R )‐valine‐derived ( R )‐ α , α ‐dimethyl‐4‐isopropyl‐4,5‐dihydrooxazole‐2‐methanol gives better results than the ( R , R , S )‐isomer ( 7d vs. 7c in Scheme 3 ), and an i‐Pr group on the 4,5‐dihydrooxazole ring gives rise to a slightly better selectivity than a Ph group. With the ( R , R , R )‐ligands the hydrogen transfer occurs from the Re face of the oxo groups ( Scheme 4 ).