Direct catalytic synthesis of enantiopure 5-substituted oxazolidinones from racemic terminal epoxides
(Chemical Equation Presented) A venerable scaffold for asymmetric synthesis and drug development, chiral 5-substituted oxazolidinones are obtained in almost enantiomerically pure form (up to 99.9% ee) starting from racemic terminal epoxides. The salient features of this process include the very simple and convenient experimental protocol and the employment of a readily accessible catalyst and inexpensive, easily handled starting materials. An enantioconvergent approach for the total conversion of racemic epoxide into a single stereoisomeric oxazolidinone is also described.
Diastereo- and enantioselective synthesis of vicinal amino alcohols by oxa Michael addition of N-formylnorephedrine to nitro alkenes
The first intermolecular asymmetric oxa Michael additions with removable chirality information within the hydroxide source are reported. As enantiopure oxygen nucleophile functioning as chiral hydroxide equivalent N-formylnorephedrine (7) was used and conjugate additions to aliphatic (E)-nitro alkenes 2a-j were carned out in good yields (35-87%) and excellent diastereomeric excesses (de = 94-≥98%). After reduction of the nitro group and protection of the amino function (11a-h, 73-87%, both steps), the cleavage of the auxiliary occurred without epimerisation (69-99%) using Na/NH3. The Boc-protected 2-amino alcohols 12a-h could be obtained in good overall yields (30-58 %, four steps) and excellent diastereomeric and enantiomeric excesses (de, ee = 94-≥98%). Transition states explaining the overall stereochemical outcome are presented based on the absolute configuration determined by X-ray structure analysis on 8b.
Enders, Dieter,Haertwig, Andreas,Raabe, Gerhard,Runsink, Jan
p. 1771 - 1792
(2007/10/03)
Enantioselektive Synthese von vicinalen Aminoalkoholen durch Oxa-Michael-Addition