Chem. Sci. http://doi.org/bj6v (2016)
Many sequential chemical reactions cannot be performed in the same vessel as they require chemically incompatible reagents or catalysts. However, chemists have devised ways in which otherwise incompatible catalytic groups can be kept spatially separated by using specific porous substrates, such as molecular organic frameworks, and some examples of one-pot orthogonal reactions have been reported. Now, Beatriu Escuder at the Universitat Jaume I in Spain and Jan van Esch and co-workers at the Delft University of Technology in The Netherlands have extended this approach to supramolecular hydrogels.
The authors targeted a tandem reaction: an acid-catalysed acetal deprotection followed by a base-catalysed aldol condensation. The two catalytic groups, a carboxylic acid and a chiral amine, respectively, are incorporated in the structural motif of two distinct hydrogelators. In solution, these hydrogelators assemble to form spatially separated networks so that the nominally incompatible — acidic and basic — reactions do not interfere with one other and proceed in tandem. In the presence of a protected acetal and a ketone as substrates, Escuder and co-workers report an 85% yield of the final aldol condensate with high enantioselectivity.