Pyrrole-Based Anion-Responsive π-Electronic Molecules as Hydrogen-Bonding Catalysts.

The abilities of dipyrrolyldiketone boron complexes as hydrogen-bonding donor organocatalysts were examined by the Mannich-type reaction of N-acyl heteroarenium chlorides with 1-methoxy-2-methyl-1-trimethylsiloxy-1-propene, as well as by the classical N-alkylation of amines with trityl chloride under base-free conditions. 1H NMR examinations of the hydrogen-bonding interaction between the pyrrole NH of the catalyst and the Cl- in the N-acyl heteroarenium salt suggested that the activation of N-acyl heteroarenium chlorides occurs through anion binding by the catalyst.