Polymer-bound lithiumamides were used in an aldol reaction. The introduction of a spacer between the polymer backbone and the reactive site was important to enhance yields of the aldol products. The polymer-bound reagent was repeatedly used in the same reaction after the conversion to the lithium amide.
Stereoselective addition of organometallic reagents to β-hydroxyketones
作者:José Luis Garcia Ruano、Amelia Tito、Rafael Culebras
DOI:10.1016/0040-4020(95)01048-3
日期:1996.2
Reactions of several β-hydroxyketones with different methylation reagents are reported. The de's are moderated or good (40–75%) and slightly change with the relative steric size of the R groups at the starting hydroxyketone. The syn-diols are predominant in reactions with Me3Al/ZnBr2 and MeLi/Me3Al, whereas the anti-diols are the major ones with MeLi/ZnBr2. The method has been used to synthesize optically
Cross-linked polymer-bound lithium dialkylamides were employed in crossed aldol reaction of various carbonyl compounds with aldehydes to afford the corresponding beta-hydroxycarbonyl compounds. The introduction of spacer chains to the polymer-bound lithium dialkylamide between the base moiety and the polystyrene backbone effectively enhanced yields of the desired aldol adducts. Sometimes better yields were obtained by using the polymer-bound reagent having an appropriate spacer-chain with those obtained using lithium diisopropylamide under homogeneous conditions. Repeated use of these polymeric reagents was demonstrated with no loss of efficiency. (C) 2004 Elsevier Ltd. All rights reserved.
KACHALKOV V. P., XIMIYA EHLEMENTOORGAN. SOEDIN. 2, 4, 5, 6 GRUPP PERIODICH. SISTEMY, PERM,+