Stereoselective radical azidooxygenation of alkenes
Radical azidooxygenation of various alkenes is described. A readily prepared N3-iodine(III) reagent acts as a clean N3-radical precursor. Radical generation is achieved with TEMPONa acting as a mild organic reducing reagent. The C-radical generated after N3-radical addition is efficiently trapped by in situ generated TEMPO. Yields are good to excellent, and for cyclic systems azidooxygenation occurs with excellent diastereoselectivity.
Zhang, Bo,Studer, Armido
p. 4548 - 4551
(2013/09/24)
General and efficient α-oxygenation of carbonyl compounds by TEMPO induced by single-electron-transfer oxidation of their enolates
A generally applicable method for the synthesis of protected α-oxygenated carbonyl compounds is reported. It is based on the single-electron-transfer oxidation of easily generated enolates to the corresponding α-carbonyl radicals. Coupling with the stable free radical TEMPO provides α-(piperidinyloxy) ketones, esters, amides, acids or nitriles in moderate-to-excellent yields. Enolate aggregates influence the outcome of the oxygenation reactions significantly. Competitive reactions have been analyzed and conditions for their minimization are presented. Chemoselective reduction of the products led to either N-O bond cleavage to α-hydroxy carbonyl compounds or reduction of the carbonyl functionality tomonoprotected 1,2-diols or O-protected amino alcohols. The oxygenation of enolates proves to be the most general and effective methodology for the synthesis of O-protected α-oxy carbonyl compounds and nitriles A. The scope and limitations of the electron-transfer-induced radical coupling reaction with TEMPO are presented. The reaction pathways are outlined. Methods for the deprotection to α-hydroxy carbonyl compounds B are provided and discussed. Copyright
Dinca, Emanuela,Hartmann, Philip,Smrcek, Jakub,Dix, Ina,Jones, Peter G.,Jahn, Ullrich
supporting information
p. 4461 - 4482
(2012/10/30)
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