Stereo–Chemical Control of Organic Reactions in the Interlamellar Region of Cation–Exchanged Clay Minerals

Abstract

Carbene intermediates can be generated by thermal, photochemical and transition metal catalysed processes from diazoalkanes. The carbene intermediates are very reactive and can add across double bonds to give 3-membered rings (cyclopropanes), insert into OH bonds to give esters and insert into neighbouring C-H bonds to give 4 or 5-membered rings, such as - and -lactams or  lactones. Copper salts and complexes were amongst the first catalysts to be used for carbene generation from diazoalkanes. However, current tendencies are to use very expensive, especially, platinum group salts and complexes to generate the carbene intermediates, as yields and specificity tend to be higher. We have found. On the other hand, that Cu (II) exchanged clay minerals, e.g. Wyoming bentonite, have proven to be very competitive in yield with these transition metal catalysts and they have the added tendency that the restricted reaction space within the clay interlayer favours the more planar/less bulky product when the layer spacing is kept low by judicious choice of solvent.
Herein we report a wide range of carbene addition (cyclopropane formation) and C-H insertion reactions (-lactam, -lactam and -lactone formation) catalysed by the Cu(II) exchanged clay minerals and the stereochemical consequences of carrying out the reactions within the clay interlayer