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Synthesis 2018; 50(14): 2721-2726
DOI: 10.1055/s-0037-1609966
DOI: 10.1055/s-0037-1609966
paper
Stereoselective Oxidation of Titanium(IV) Enolates with Oxygen
Financial support from the Spanish Ministerio de Economía y Competitividad (Grant No. CTQ2015-65759-P) and the Generalitat de Catalunya (2014 SGR586 and 2017SGR 271) as well as a doctorate studentship to A.G.-P. (APIF, Universitat de Barcelona) are acknowledged.Further Information
Publication History
Received: 13 March 2018
Accepted after revision: 13 April 2018
Publication Date:
29 May 2018 (online)
Abstract
A novel approach to synthesize enantiomerically pure α-hydroxy carboxylic derivatives is reported. A highly stereoselective oxidation of titanium(IV) enolates from chiral N-acyloxazolidinones is performed with oxygen under simple experimental conditions that do not require any reducing steps. The success of this approach depends on the biradical character of titanium(IV) enolates.
Key words
stereoselective synthesis - hydroxylation - titanium enolates - chiral auxiliaries - oxygen - radicalsSupporting Information
- Supporting information for this article is available online at https://doi.org/10.1055/s-0037-1609966.
- Supporting Information
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Zakarian has convincingly demonstrated the biradical character of titanium(IV) and zirconium(IV) enolates in highly stereoselective reactions:
Enolization with mild titanium(IV) Lewis acids is only possible in more acidic α-halo or α-aryl substrates. See, for instance:
Stereoselective oxidation of enolates by peroxide intermediates has been occasionally proposed in α-hydroxylation reactions with molecular oxygen. See, for instance:
For the role of peroxide intermediates in nonstereoselective hydroxylation of enolates with molecular oxygen, see:
For the removal of 5,5-disubstituted oxazolidinones, see: