The use of lithium salts of weakly coordinating anions in the catalysis of organic transformations

I. Intramolecular Diels-Alder reactions in lithium perchlorate-diethyl ether. Intramolecular Diels-Alder reactions were investigated using concentrated (5 Molar) solutions of lithium perchlorate in diethyl ether as the solvent. The addition of a catalytic amount of a Bronsted acid enhanced both rates and endo/exo selectivities. In the case of conformationally demanding substrates, terminal dienes were found to migrate in by one carbon prior to cycloaddition.;II. Ionic Diels-Alder reactions in lithium perchlorate-diethyl ether. The use of concentrated (4 or 5 Molar) solutions of lithium perchlorate in diethyl ether with the addition of a catalytic amount of a Bronsted acid such as camphorsulfonic acid as a reaction medium for ionic Diels-Alder reactions was investigated. A number of reactions involving acetals, ketals, and orthoesters in both inter and intramolecular cycloadditions were successful using these conditions.;III. Lithium triflimide in diethyl ether or acetone as a safe alternative to lithium perchlorate in the catalysis of organic reactions. Due to the known hazards involved in the use of perchlorates, several alterative lithium salts were investigated. Concentrated (4 Molar) solutions of lithium bis(trifluoromethanesulfonyl)imide (triflimide) in diethyl ether or acetone proved to exhibit similar rate and selectivity enhancements of Diels-Alder reactions when compared to the same reactions using 5 Molar lithium perchlorate in diethyl ether.;IV. The use of lithium and magnesium salts in weakly coordinating solvents as catalysts for organic reactions. The use of substoichiometric amounts of lithium or magnesium salts in weakly coordinating solvents such as methylene chloride or even toluene to catalyze Mukaiyama-Michael additions and the ionization and nucleophilic trapping of allylic acetates was investigated. Magnesium triflimide in methylene chloride and lithium tetrakis(1,1,1,3,3,3-hexafluoro-2-phenyl-2-propyloxy)aluminate in toluene proved to be particularly active as catalysts.