Product diversity in cyclisations of maleamic acids: the imide–isoimide dichotomy
摘要:
Cyclisation of maleamic acids with acetic anhydride in dimethylacetamide (DMA) at ca. 75 degrees C, with or without added cobalt naphthenate, gives predominantly maleimides when the parent maleic anhydride is unsubstituted. However, when the maleic anhydride has either one or two methyl substituents, the products are greater than or equal to 95% maleisoimides (5-imino-2,5-dihydrofuran-2-ones). In contrast all maleamic acids investigated, regardless of the extent of substitution, give exclusively maleimides when heated in acetic acid under reflux. Isoimide formation in the Ac2O-DMA-cobalt naphthenate procedure appears to arise from kinetic control, since the isoimide preference was reduced at higher reaction temperature. The preferred Z-stereochemistry of the isoimide 3 is confirmed by X-ray crystallography.
The action of amines on citraconic anhydride. X-Ray crystal structure of (Z)-2-methyl-3-pyrrolidinocarbonylpropenoic acid
作者:Ahmet E. Baydar、Gerhard V. Boyd、John Aupers、Peter F. Lindley
DOI:10.1039/p19810002890
日期:——
The reaction of citraconic anydride with 15 primary and secondary amines gave mixtures of isomeric citraconamic acids (2) and (3), in which the former predominated. The more abundant isomers rearranged to the thermodynamically stable N-substituted (Z)-2-methyl-3-carbamoylpropenic acids (3) on warming. The structure of the pyrrolidide (3q) was confirmed by X-ray analysis. An unsuccessful attempt to