Issue 1, 2022

One-pot enantioselective construction of 3,4-dihydro-2H-1,4-oxazines over Ru/Au relay catalysis and its mechanistic serendipity

Abstract

The preparation of enantiomerically pure 1,4-oxazines remains a continuous challenge in synthetic chemistry because of their potential application in the total synthesis of morpholines. Herein, a one-pot asymmetric transfer hydrogenation/cyclization enantio-relay process catalyzed by Ru and Au bimetallic catalysts was developed. This enantio-relay process firstly allows the asymmetric transfer hydrogenation of alkynones to form chiral alkynols in the presence of (S,S)-mesityleneRuClTsDPEN (TsDPEN = N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine) and then the chiral alkynols could be converted into 3,4-dihydro-2H-1,4-oxazines in moderate to good yields with excellent enantioselectivity retention accompanied by AuCl(PPh3)/AgNTf2 and HCOOH. A series of sulfonamide-tethered alkynones were well tolerated in this process. Mechanistic studies indicated that the alkynols formed in the first step were initially transformed into a methylenemorpholine intermediate when AuCl(PPh3)/AgNTf2 and HCOOH were added, which can be further isomerized into chiral 3,4-dihydro-2H-1,4-oxazines with the addition of a second HCOOH. This protocol offers not only a practical method to access 3,4-dihydro-2H-1,4-oxazines from alkynones in an enantioselective version, but also enriches the arsenal of gold chemistry from a mechanistic point of view.

Graphical abstract: One-pot enantioselective construction of 3,4-dihydro-2H-1,4-oxazines over Ru/Au relay catalysis and its mechanistic serendipity

Supplementary files

Article information

Article type
Research Article
Submitted
01 Oct 2021
Accepted
04 Nov 2021
First published
17 Nov 2021

Org. Chem. Front., 2022,9, 102-108

One-pot enantioselective construction of 3,4-dihydro-2H-1,4-oxazines over Ru/Au relay catalysis and its mechanistic serendipity

D. Yang, C. Wang, Y. Wang, G. Liu, T. Cheng and R. Liu, Org. Chem. Front., 2022, 9, 102 DOI: 10.1039/D1QO01482J

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