116836-45-4Relevant articles and documents
STEREOSELECTIVE ALDOL REACTIONS VIA TITANIUM ENOLATES
Murphy, Patrick J.,Procter, Garry,Russell, Andrew T.
, p. 2037 - 2040 (1987)
The species produced by treatment of the lithium enolate of N-propionylpyrrolidine with bis(cyclopentadienyl)titanium dichloride adds to simple aldehydes with high stereoselectivity to give anti-aldol products.
Enantioselective aldol and Michael additions of achiral enolates in the presence of chiral lithium amides and amines
Juaristi,Beck,Hansen,Matt,Mukhopadhyay,Simson,Seebach
, p. 1271 - 1290 (2007/10/02)
It is now well established that lithium enolates and analogous derivatives generally exist as complex structures held together by noncovalent bonds ('supramolecules'). In particular, Li enolates aggregate to give dimers, tetramers, and higher oligomers, whose metal centers may be complexed by solvent molecules or chelating ligands. In addition, the anionoid part of the enolates may hydrogen-bond to weak acids such as secondary amines. Furthermore, such supramolecules can be product-forming species in synthetic reactions of Li enolates. This paper describes our observations of the temporary incorporation of chiral amines or chiral lithium amides into achiral lithium enolate aggregates (an interaction which is simply broken during aqueous workup!) to give enantiomerically enriched products. In particular, enantioselective aldol and Michael additions between achiral enolates and achiral aldehydes or achiral nitroolefins have been achieved in the presence of several chiral amines (or their lithium amides) derived from (S)-valine or (R,R)-tartaric acid. Finally, this report demonstrates the potential usefulness in asymmetric synthesis of ortho lithiation directed by chiral α-aminoalkoxides.
Fluoride Ion Catalyzed Reduction of Aldehydes and Ketones with Hydrosilanes. Synthetic and Mechanistic Aspects and an Application to the Threo-Directed Reduction of α-Substituted Alkanones
Fujita, Makoto,Hiyama, Tamejiro
, p. 5405 - 5415 (2007/10/02)
Reduction of aldehydes and ketones with hydrosilanes proceeded in the presence of a catalytic amount of tetrabutylammonium fluoride or tris(diethylamino)sulfonium difluorotrimethylsilicate in aprotic polar solvents under mild conditions.A significant isotope effect (kH/kD = 1.50) was observed in competitive reduction of acetophenone with HSiMe2Ph and DSiMe2Ph.The reaction was of first order in the concentration of an aprotic polar solvent HMPA.Reduction of 2-methylcyclohexanone gave cis-2-methylcyclohexanol with selectivities up to 95percent.The kinetic and stereochemical results suggest that a hexavalent fluorosilicate - is involved. α-Alkoxy (acyloxy or dimethylamino) ketones were transformed to threo alcohols in high diastereoselectivities.The reduction was also applied to α-methyl-β-keto amides, RCOCH(MeCONR)2, to afford the corresponding threo alcohols in >98percent selectivity.The threo selectivity is explained in terms of the Felkin-Anh model in which interaction of carbonyl oxygen with a countercation is ideally suppressed.The threo-directed reduction was applied to (R)-1-phenyl-4-(2-tetrahydropyranyloxy)-1-penten-3-one and N-(2-benzoylpropanoyl)piperidine.The resulting threo alcohols were respectively converted into (2R,3S)-2,3-(cyclohexylidenedioxy)butanal, a key intermediate of daunosamine synthesis, and into a pharmacologically useful compound threo-N-(3-hydroxy-2-methyl-3-phenylpropyl)piperidine.
