- Highly enantioselective iridium-catalyzed hydrogenation of α,β-unsaturated esters
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α,β-Unsaturated esters have been employed as substrates in iridium-catalyzed asymmetric hydrogenation. Full conversions and good to excellent enantioselectivities (up to 99 % ee) were obtained for a broad range of substrates with both aromatic- and aliphatic substituents on the prochiral carbon. The hydrogenated products are highly useful as building blocks in the synthesis of a variety of natural products and pharmaceuticals. Asymmetric hydrogenation: A variety of α,β-unsaturated esters were hydrogenated with high enantioselectivities (see scheme). The hydrogenated products have been used in synthetic transformations as well as in formal total syntheses. Copyright
- Li, Jia-Qi,Quan, Xu,Andersson, Pher G.
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p. 10609 - 10616
(2012/11/07)
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- Synthesis and utility of the 3,3-dimethyl-5-substituted-2-pyrrolidinone 'Quat' chiral auxiliary
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The synthesis and utility of the 3,3-dimethyl-5-substituted-2-pyrrolidinone 'Quat' chiral auxiliary in stereoselective enolate reactions of attached N-acyl side chains combined with the mild and non-racemising conditions required for the ultimate removal of the chiral side chain is described.
- Davies, Stephen G.,Dixon, Darren J.,Doisneau, Gilles J.-M.,Prodger, Jeremy C.,Sanganee, Hitesh J.
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p. 647 - 658
(2007/10/03)
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- Asymmetric aldol and alkylation reactions mediated by the 'quat' chiral auxiliary (R)-(-)-5-methyl-3,3-dimethyl-2-pyrrolidinone
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Enolates derived from the N-propionoyl derivative of the 'quat' chiral auxiliary (R)-(-)-5-methyl-3,3-dimethyl-2-pyrrolidinone undergo highly stereoselective aldol and alkylation reactions. Removal of the auxiliary has been demonstrated with LiOH, PhCH2OLi, MeOMgBr and LiAlH4 to generate respectively (2R,3R)-3-hydroxy-2-methyl-3-phenylpropionic acid in homochiral form, and with 96% e.e. (S)-2-methyl-3-phenylpropionic acid and derived methyl and benzyl esters and with >94% e.e. (S)-2-methyl-3-phenylpropanol.
- Davies,Doisneau,Prodger,Sanganee
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p. 2373 - 2376
(2007/10/02)
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- Enantiospecific preparation of [(2R,6S)-endo]-5-aza-1,10,10-trimethyl-3-oxatricyclo[5.2.1.02,6)]de can-4-one by a nitrene-mediated route from [(1S]-endo]-(-)-borneol and its utility as a chiral auxiliary in some asymmetric transformations
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Attempted chiral aziridination of styrene by addition of optically-active alkoxycarbonylnitrene 5 derived from [(1S)-endo]-(-)-bornyl p-nitrobenzenesulphonoxycarboxy 4 is reported. No measurable asymmetric induction is observed under the various conditions employed, but in the absence of alkene, a tricyclic oxazolidin-2-one 8 is formed to which preparatively simpler access can be gained by thermal decomposition of azidoformate 7, either in 1,1,2,2-tetrachloroethane (50%) or by spray pyrolysis (58%). The oxazolidin-2-one 8 is demonstrated to be a successful chiral auxiliary by contemporary standards in a variety of asymmetric transformations, including alkylation, acylation, and aldol reactions for which high levels of asymmetric induction are observed. Diethylaluminium chloride catalysed Diels-Alder reactions exhibit poorer selectivity except for the cinnamoyl derivative 23 which is stereospecific.
- Banks,Blake,Cadogan,Dawson,Gosney,Grant,Gaur,Hodgson,Knight,Smith,Stevenson
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p. 7979 - 8006
(2007/10/02)
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