- Total regioselective and diastereospecific iodolysis of 2,3-epoxyamides promoted by SmI2: Synthesis of (2R*,3R*)- or (2R*,3S*)-2-hydroxy-3-iodoamides
-
The use of samarium diiodide as a source of iodides is reported. Thus, 2-hydroxy-3-iodoamides were obtained, with total regioselectivity, by treatment of 2,3-epoxyamides, in which the oxirane ring is 2,3-disubstituted or 2,2,3-trisubstituted, with SmI2. The ring-opening reaction was diastereospecific and (2R*,3R*)- or (2R*,3S*)-2-hydroxy- 3-iodoamides were obtained from cis- or trans-epoxyamides, respectively. The relative configuration of 2-hydroxy-3-iodoamides was established by X-ray analysis. A mechanism to explain this transformation has been proposed. The starting compounds 1 are easily prepared by the reaction of enolates derived from 2-chloroamides with aldehydes at -78°C.
- Concellon, Jose M.,Bardales, Eva,Concellon, Carmen,Garcia-Granda, Santiago,Diaz, M. Rosario
-
-
Read Online
- Diastereoselective darzens condensations of α-haloamides: Influence of aryl substituents on diastereoselectivity
-
N, N-Diaryl α-haloamides undergo Darzens condensations with aldehydes induced by metal hydroxides. The diastereoselectivity of epoxide formation is strongly influenced by the electronic properties of the arylamide, which can be rationalised on the basis of the acidity of the substrate hydrogens and hence on reaction occurring under kinetic or thermodynamic control.
- North, Michael,Pizzato, Francesca
-
experimental part
p. 552 - 556
(2010/04/23)
-
- A stereocontrolled approach to electrophilic epoxides
-
Lithium t-butyl hydroperoxide (easily generated by addition of an alkyl-lithium to anhydrous t-butyl hydroperoxide in THF solution) is a powerful reagent for the epoxidation of electrophilic alkenes at -20 to 0 °C under full stereocontrol. Thus αβ-unsaturated esters, sulphones, sulphoximines, and amides are readily epoxidised with complete regio- and stereo-specificity and with considerable chiroselectivity (20-100%) when appropriate chiral auxiliaries such as menthyl, 8-phenylmenthyl, or a camphor-sulphonamide derivative are used. Asymmetric αβ-unsaturated sulphoximines undergo epoxidation with 100% diastereoselectivity. The only exceptions to stereocontrol noted are heavily substituted maleate esters such as di-t-butyl maleate. The αβ-epoxy amides are shown to be valuable sources of the corresponding epoxy ketones by treatment with an organolithium, allowing a stereo- and chemoselective entry in high yield to these useful intermediates.
- Meth-Cohn, Otto,Moore, Clive,Taljaard, Heinrich C.
-
p. 2663 - 2674
(2007/10/02)
-