Intermolecular Diels-Alder reactions aqueous

Grieco utilized an aqueous intermolecular Diels-Alder reaction as the key step in forming the AB ring system of the potent cytotoxic sesquiterpene vernolepin. 87 Cycloaddition of sodium ( >3,5-hexa-dienoate with an a-substituted acrolein in water followed by direct reduction of the intermediate Diels-Alder adduct gave the desired product in 91% overall yield (Eq. 12.28). 

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. 

Nitrocoumarins underwent intermolecular Diels-Alder reaction with substituted dienes, followed by sequential hydrolysis / decarboxylation / Nef reaction / cyclodehydration to afford dihydrodibenzo[f>,. 

In the examples cited so far, the controlling chirality has been localized on the dienophile component. It is also possible to construct chiral dienes that are capable of inducing asymmetry in intermolecular aqueous Diels-Alder reactions. For example, the chiral cyclic diene 4.30 - readily obtained via enzymatic oxidation of 7-phenylnorbomadiene - has been shown to be a good partner for asymmetric aqueous Diels-Alder reactions [55]. Thus, diene... 

Grieco, P.A. Yoshida, K. Garner P., Aqueous intermolecular Diels-Alder chemistry reactions of diene carboxylates with dienophiles in water at ambient temperature, J. Org. Chern., m, 26,3137-9. 

Grieco, P.A. Galatsis, P. Spohn, R.F., Aqueous intermolecular Diels-Alder chemistry. Reaction of ( )-2,4-pentadienyl ammonium chloride and related ammonium salts with dienophiles in water. Tetrahedron, 1986,42,2847-53. 

AppUcations of the aqueous iminium-ion-based Diels-Alder reaction to more demanding systems have also been explored. One area of investigation centered on the reaction between iminium ions and stabilized diene systems. Initial attempts to effect intermolecular iminium-ion-based [4+2] cycloadditions with styrenes under the standard conditions failed, yielding only by-... 

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