Isoinversion effect

Samarium iodobinaphtholate (222) has been reported to act as an efficient enantioselective catalyst for the Michael addition of aromatic amines to fumaryl oxazolidinone (220), affording the aspartic acid derivatives (221) in good yields. Elucidation of the influence of temperature on the addition of p-anisidine revealed an isoinversion effect with a maximum ee of 88% at —40 °C.257 A non-enantioselective version of this reaction has also been reported.258... 

Imidazolide ionic liquids [Bmimjlm (2 mol%) have been reported to catalyse aza-Michael addition of, for example, imidazole to acrylates and acrylonitriles. Samarium diiodide has been identified as an efficient catalyst for the aza-Michael addition of 0-benzylhydroxylamine to a,/8-unsaturated Af-acyloxazolidinones. The 1,1-bi-2-naphthol (BINOL)-Sml complex afforded the Michael adducts with <88% ee. An isoinversion effect with temperature was observed for the highest enantiomeric excess at -40°C.205... 

An interesting result has been obtained with respect to the stereoselectivity of the addition of benzoyl nitrene to compounds 104a-104d The ratio of the two diastereomers depends on the temperature, such that an inversion of the diastereoselectivity can be observed at a distinct temperature (isoinversion principle [47]). Such an effect may indicate a reversible first bond formation between the benzoyl nitrene and the alkene [45]. 

Based on the pioneering study of the influence of the reaction temperature on diastereoselectivity137, 138, it is now known that enthalpy and entropy effects oppose each other in the transformation of 1 to 2136. Comparison of different systems at a single temperature may therefore be meaningless, since the results obtained below an isoselective temperature140 will be reversed above that temperature136. This principle of isoinversion may have to be taken into account in a comprehensive discussion of the above reactions141. 

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