Clays as selective catalysts in organic synthesis

Suitably modified smectite clays can be very selective catalysts for a wide range of organic reactions. While it has long been known that such materials can act as Bronsted and Lewis acids, it has been shown recently that they are also effective Diels-Alder catalysts. A selection of illustrative reactions is given which emphasises their wide range of use, their selectivity, and the ease of work-up after reaction. In each case, mechanistic information is presented, e.g., on the site of reaction (whether interlayer or surface), rate determining steps, etc. The regiochemical consequences of the restricted reaction space are stressed.Based on material presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.