Organic Synthesis in Clay Nanospaces

Abstract

From a viewpoint of synthetic organic chemistry is discussed acid catalysis of ion-exchanged clay montmorillonites in some carbon-carbon bond-forming reactions, compared with acid catalysis of conventional homogeneous acids such as CF3SO3H and BF3·OEt2. Acidity of clay depends on the sort of cations exchanged in the clay. Tin (IV), iron (III), and aluminum (III) ion-exchanged montmorillonites show very strong acidity in organic media, promoting the carbon-carbon bond formation involving the reactions of carbonyl compounds with silicon nucleophiles such as cyanotrimethylsilane and silicon enolates. Sulfuric acid-treated montmorillonite, K 10 has been found to have mesopores in nanometers, acting as a suitable template to produce meso-tetraalkylporphyrins from aliphatic aldehydes and pyrroles via oligomerization and intramolecular cyclization in the nanospaces. The advantage of using solid acids over using homogeneous acids in organic synthesis is mentioned as well. © 1995, The Society of Synthetic Organic Chemistry, Japan. All rights reserved.