Asymmetric Synthesis of 2H‐Azirines with a Tetrasubstituted Stereocenter by Enantioselective Ring Contraction of Isoxazoles. Issue 4 (12th December 2017)

• Record Type: Journal Article
• Authors: Okamoto, Kazuhiro; Nanya, Atsushi; Eguchi, Akira; Ohe, Kouichi
• Is Part Of: Angewandte Chemie international edition. Volume 57:Issue 4(2018)
• Page Start: 1039
• Page End: 1043
• Publication Date: 2017-12-12
• Subjects: 2H-azirines -- chiral diene ligands -- isoxazoles -- nitrogen heterocycles -- rhodium catalysis; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201710920
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Highly strained 2 H ‐azirines with a tetrasubstituted stereocenter were synthesized by the enantioselective isomerization of isoxazoles with a chiral diene–rhodium catalyst system. The effect of ligands and the coordination behavior support the proposed catalytic cycle in which the coordination site is fixed in favor of efficient enantiodiscrimination by a bulky substituent of the ligand. In silico studies also support the existence of a rhodium–imido complex as a key intermediate for enantiodiscrimination. Abstract : Coping well under the strain : Highly strained 2 H ‐azirines with tetrasubstituted stereocenters were synthesized with high enantioselectivity by the N−O bond‐cleaving isomerization of isoxazoles in the presence of a chiral diene–rhodium catalyst (see scheme). This asymmetric ring contraction of isoxazoles proceeded under mild reaction conditions to give 2‐alkoxycarbonyl 2 H ‐azirines with various substituents, including halogen groups.