Diels Alder reactions rates

Diels-Alder reactions rate acceleration promoted by a bisphenylendiol [93c]... 

Scheme 5.10 Enhancement of Diels-Alder reaction rates in water...

Uncatalysed Diels-Alder reactions usually have to be carried out at relatively high temperatures (normally around 100 °C)73, often leading to undesired side reactions and retro-Diels-Alder reactions which are entropically favoured. The Diels-Alder reaction became applicable to sensitive substrates only after it was realized that Lewis acids (e.g. A Clg) are catalytically active56. As a consequence, Diels-Alder reactions can now be carried out at temperatures down to — 100°C85. The use of Lewis acid catalysts made the [4 + 2]-cycloaddition applicable to the enantioselective synthesis of many natural compounds51,86. Nowadays, Lewis acid catalysis is the most effective way to accelerate and to stereochemically control Diels-Alder reactions. Rate accelerations of ten-thousand to a million-fold were observed (Table 7, entries A and B). 

Grieco, P. A. Giamer, P. He, Z.-M. "Micellar" catalysis in the aqueous intermolecular Diels-Alder reaction Rate acceleration and enhanced selectivity, Tetrahedron Lett. 1983, 24,1897-1900. 

During the parameter estimation, it was noted that the model is relatively insensitive to changes in k, and therefore it should not be taken as a reliable prediction of the Diels-Alder reaction rate constant. Effectively, the rate R is very large compared with the rates of initiation and chain transfer, and therefore the DH ratio calculation could be simplified without significantly changing the model results ... 

Diels-Alder reaction. Rate enhancement of the Diels Alder reaction is noted in aqueous perfluorinated emulsions (from perfluorohexane and hthium perfluorooctane-sulfonate) ... 

Kelly, T.R., Meghani, P. and Ekkundi, V.S. (1990) Diels-Alder reactions rate acceleration promoted by a biphenylenediol. Tetrahedron Letters, 31, 3381-3384. 

Reactivities in Diels-Alder Reactions Rates of Diels-Alder reactions are affected by steric as well as electronic factors. For Diels-Alder reaction to proceed dienes must have double bonds on the same side of central-single bond, i.e. there must be c/s-conformation because this is high energy conformation. 

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