41918-08-5Relevant articles and documents
Solid-state and solution structures of several new [LnCp′2(OR)]2 complexes (Ln=Pr, Yb) with chiral, oxygen-functionalized μ-alkoxide ligands
Steudel, Annette,Stehr, Jens,Siebel, Eric,Fischer, R. Dieter
, p. 89 - 96 (1998)
Nine novel organolanthanoid (Ln=Pr and Yb) complexes of the general type [LnCp′2(μ-OCHR(1)Z)]2 (Cp′=C5H5 or CH3C5H4, R(1)=H or Me) containing exclusively ch
A highly stereoselective ether directed palladium catalysed aza-Claisen rearrangement
Jamieson, Andrew G.,Sutherland, Andrew
, p. 735 - 736 (2007/10/03)
A highly stereoselective rearrangement of allylic trichloroacetimidates to allylic trichloroamides has been achieved using adjacent ether groups to direct facial coordination of the palladium(II) catalyst. The Royal Society of Chemistry 2005.
Product studies and laser flash photolysis on alkyl radicals containing two different β-leaving groups are consonant with the formation of an olefin cation radical
Bales,Horner,Huang,Newcomb,Crich,Greenberg
, p. 3623 - 3629 (2007/10/03)
1-Bromo-2-methoxy-1-phenylpropan-2-yl (3) and 2-methoxy-1-phenyl-1-diphenylphosphatopropan-2-yl (4) were generated under continual photolysis from the respective PTOC precursors in a mixture of acetonitrile and methanol. The radicals undergo heterolytic fragmentation of the substituent in the β-position to generate the olefin cation radical (5). Z-2-Methoxy-1-phenylpropene (15) is the major product formed in the presence of 1,4-cyclohexadiene, and is believed to result from hydrogen atom transfer to the oxygen of the olefin cation radical, followed by deprotonation. Laser flash photolysis experiments indicate that reaction between 5 and 1,4-cyclohexadiene occurs with a rate constant of ～6 × 105 M-1 s-1. 2,2-Dimethoxy-1-phenylpropane (18) is observed as a minor product. Laser flash photolysis experiments place an upper limit on methanol trapping of 5 at k 3 M-1 s-1 and do not provide any evidence for the formation of reactive intermediates other than 5. The use of two PTOC precursors containing different leaving groups to generate a common olefin cation radical enables one to utilize product analysis to probe for the intermediacy of other reactive intermediates. The ratio of 15:18 is dependent upon hydrogen atom donor concentration, but is independent of the PTOC precursor. These observations are consistent with the proposal that both products result from trapping of 5 that is formed via heterolysis of 3 and 4.
Syntheses of isotopically labelled L-?±-amino acids with an asymmetric centre at C-3
Harding, John R.,Hughes, Rachael A.,Kelly, Nicholas M.,Sutherland, Andrew,Willis, Christine L.
, p. 3406 - 3416 (2007/10/03)
Approaches are described to the synthesis of a series of isotopically labelled L-a-amino acids each with an asymmetric centre at C-3, including isoleucine, allo-isoleucine, threonine and allo-threonine. The methods may be simply adapted for the selective incorporation of an isotopic label at each site of L-valine including the selective labelling of either diastereotopic methyl group with carbon-13 and/or deuterium and labelling of the amine with nitrogen-15. ? The Royal Society of Chemistry 2000.
Diastereoselective Conjugate Addition to (+)-Camphorsulfonic Acid Derived Nitroalkenes: Synthesis of α-Hydroxy and α-Amino Acids
Barrett, Anthony G. M.,Braddock, D. Christopher,Christian, Paul W. N.,Pilipauskas, Daniel,White, Andrew J. P.,Williams, David J.
, p. 5818 - 5823 (2007/10/03)
Diastereoselective tandem conjugate addition of both oxygen- and nitrogen-centered nucleophiles to the novel (1S)-10-camphorsulfonic acid derived nitroalkenes 9, 10, and 11 and ozonolysis gave the α-hydroxy and α-amino thiol acid derivatives 12, 13, and 14. In all cases, the (R)-diastereomer was formed as the major component albeit with only modest levels of selectivity (33-71% de). The structures of the products and the stereochemistry of the Michael addition step were unequivocally established by X-ray crystallographic studies of nitroalkenes 9 and 10 and (2S)-12c and (2R)-13a and by alternative syntheses from (S)-alanine, (S)-valine, and ethyl (S)-lactate.
Asymmetric Synthesis of Organosilicon Compounds Using a C2 Chiral Auxiliary
Kobayashi, Kimiko,Kato, Takayuki,Unno, Masafumi,Masuda, Shinji
, p. 1393 - 1401 (2007/10/03)
Optically active silanes were synthesized by a novel asymmetric synthesis which involved the diastereoselective ring-opening reaction of 1,3-dioxa-2-silacycloheptanes bearing a C2 chiral auxiliary with Grignard reagents, followed by a lithium aluminum hydride (LiAlH4) reduction. (R)-Ethylmethylphenylsilane and (R)-methylphenylpropylsilane were derived in 93%ee and 98%ee, respectively. The preparation of the other optical silanes is also described. The maximum rotations of some of them have been determined by 1H NMR and/or capillary GC methods. A mechanism for a diastereoselective ring-opening reaction is proposed based on the stereochemical results.
On enantioselective separation of phenoxypropionates using permethylated β-cyclodextrin HPLC and GC columns
Weber,Kreuzig,Bahadir
, p. 13 - 20 (2007/10/03)
Investigations on chiral phenoxypropionates using permethylated β-cyclodextrin HPLC and GC columns showed a decrease in enantioselective separation efficiency from mecoprop-methyl and dichlorprop-methyl to the threefold chlorinated fenoprop-methyl. This corresponded to decreasing electron density in the aromatic system due to the increasing negative inductive effect of 3 chlorine substituents. Investigation on methyl-(RS)-2-(2,4-dichloro-3,6-dinitrophenoxy)-propionate confirmed the influence of electrophilic substituents while determination of ethyl-(RS)-2-methoxypropionate emphasized the necessity of an aromatic system for enantioselective separation on a-cyclodextrin stationary phases. For fenoprop-methyl as well as for the aryloxyphenoxypropionates diclofop-methyl and fluazifop-butyl, reversed phase HPLC showed higher separation performance than high resolution capillary GC.
Enantioselective syntheses of α-amino-β-hydroxy acids, [15N]-L-allothreonine and [15N]-L-threonine
Sutherland, Andrew,Willis, Christine L.
, p. 1837 - 1840 (2007/10/03)
The enantioselective synthesis of [15N]-L-allothreonine from ethyl (S)-lactate via methyl (S)-3-methoxymethoxy-2-oxobutanoate 15 is described. The stereogenic centre at C-2 was established by a one-pot, dual enzyme catalysed hydrolysis of the ester (by a lipase) and reductive amination of the ketone of 15 (with leucine dehydrogenase) to give, after deprotection, [15N]-(2S,3S)-2-amino-3-hydroxybutanoic acid as a single diastereomer in 93% yield. [15N]-L-Threonine was prepared by an analogous strategy from methyl (R)-lactate using phenylalanine dehydrogenase in the reductive amination step. This approach may be simply adapted for the incorporation of deuterium and carbon-13.
Phosphane ligands with two binding sites of differing hardness for enantioselective Grignard cross coupling
Terfort, Andreas,Brunner, Henri
, p. 1467 - 1479 (2007/10/03)
A series of new, chiral phosphanes is presented, individual members of which were designed to serve as ligands in transition-metal mediated asymmetric Grignard cross coupling reactions. These ligands are characterized by a side chain containing one or two oxygen atoms with the capacity to act as binding sites for the incoming Grignard reagent. A number of structural parameters for the compounds was varied to learn about the reaction mechanism. Most of the ligands were tested in two cross coupling reactions, the formation of 3-phenylbut-1-ene and of 2,2′-dimethyl-1,1′-binaphthyl, respectively. Although both systems gave modest enantiomeric excesses it was not possible to make a comparison of their respective abilities.
