Umsetzungen der Titelverbindungen (Ia), (Ib) [dimere Formen; (Ib) steht im Gleichgewicht mit (II)] bzw. (III) [monomere Form von (Ia)] mit 2π‐, 4π‐ und ön‐Elektronen‐Addenden (Äthylene, Dione, Fulvene) werden ausführlich untersucht und anhand FMO‐theoretischer Überlegungen hinsichtlich der jeweiligen Regio‐, Stereo‐ bzw. Periselektivität eingehend mechanistisch interpretiert.
The cycloadditions of 3-hydroxy-1-methylpyridinium betaines with electron-deficient olefins have been extended to a variety of 1-substituents in place of methyl. Application of resonance theory and later of quantum chemical methods led to rationalization of preceding results and prediction of new reactions. Thermal additions of 2n-and 6n-electron addends at the 2,6-positions and of 4n-electron addends at the 2,4-positions are described. The cycloadducts are highly interesting potential synthetic building blocks.
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