3,3‘-Oxazolidinyl-Substituted 2,2‘-Biphenyldiols: Novel Tropos Ligands with a Large Induction on the Chiral Axis
摘要:
A novel type of bisphenol ligand is presented which provides high modularity. Chiral information is introduced in the 3,3 '-positions as N-arenesulfonyl-1,3-oxazolidines inducing an unexpectedly high diastereoselectivity of up to 98: 2 onto the chiral axis. The impact of each part of the molecule on the diastereomeric ratio is evaluated with extended variable-temperature (VT) NMR studies. A first example of application in asymmetric catalysis is given.
Asymmetric Strecker Reaction ofN-Benzhydrylimines Utilising New Tropos Biphenyldiol-Based Ligands
作者:Stefan Wünnemann、Roland Fröhlich、Dieter Hoppe
DOI:10.1002/ejoc.200700763
日期:2008.2
intermediates together with easily accessible N-arenesulfonylamino alcohols furnish a broad variety of 1,3-oxazolidines. These are applied as chiral tropos ligands in a titanium-mediated Strecker-type reaction of N-benzhydrylimines. A correlation between the ee values in the product and the diastereomeric ratio concerning the chiral axis of the ligand is made. Those substituents in the ligand which proved
Diastereoselective Synthesis of Enantiomerically Pure 3-Organosulfonyl-2-(2-oxocycloalkyl)-1,3-oxazolidines from 2-Formylcycloalkanones and β-Aminoalkanols
The title compounds (3-arylsulfonyl- or 3-mesyl-2-(2-oxocycloalkyl)-1, 3-oxazolidines) belonging to two different diastereomeric series, are prepared selectively by variation of the condensation conditions. By this, the chiral information of the 2-amino- 1-alkanol is extended to the cycloalkanone ring. Opposite configuration can be set up at the stereogenic center adjacent to the carbonyl group by using the same chiral auxiliary.
using hypervalent iodine reagent. A new m-CPBA mediated geminal aminooxygenation is also reported. A novel reagent-switch for the control of migrating group by controlling the two independent geminal addition paths is developed. Deuteriumlabelling studies and the control studies have provided unambiguous evidences for the phenyl migration and hydride migration in the oxidative geminal difunctionalization
Alcohol versus alcohol: A highly stereocontrolled synthesis of substituted morpholines is realized by means of gold‐catalyzed dehydrative allylic cyclization of diols (see scheme for one example; segphos = 5,5′‐bis[di(3,5‐di‐tert‐butyl‐4‐methyoxyphenyl)phosphine]‐4,4′‐bi‐1,3‐benzodioxole). The present methodology represents one of the few examples of enantioselective gold‐catalyzed transformations
Newchiralauxiliaries based on the bicyclic-isoxazolidine skeleton, 3-oxa-2,7-diazabicylo[3,3,0]octane derivatives, were synthesized in 60–80% overall yields from amino acids. Asymmetric alkylation and boron aldol reaction using the auxiliaries proceeded with high selectivities. “Carboxylic amide” has been used for the asymmetric boron-mediated aldol reaction for the first time.