Superelectrophilic Nonclassical Carbocations.

The chemistry of dicationic and tricationic 2-norbornyl cations has been studied. A series of N-heterocyclic functionalized norborneol substrates were prepared and ionization of these compounds in superacid provided superelectrophilic species. These highly charged 2-norbornyl cations were found to react with arene nucleophiles in high yields and stereoselectivity. Density functional theory computational studies suggest that increasing positive charge on the structures tends to enhance the degree of nonclassical (or 3-center-2-electron) bonding through separation of the cationic charges.

Friedel-Crafts Reactions with N-Heterocyclic Alcohols.

N-Heterocyclic alcohols are shown to be excellent substrates for superacid-promoted Friedel-Crafts reactions. The N-heterocyclic alcohols ionize to produce reactive, dicationic intermediates which provide good to excellent yields of arylation products.

Superacid Promoted Synthesis of 9,9'-Spirobifluorenes and Related Aza- and Diazaspirocycles.

A variety of 9,9'-spirobifluorenes and related azaspirocycles and diazaspirocycles have been prepared in high yields by intramolecular Friedel-Crafts reaction using the Brønsted superacid, triflic acid (CF3SO3H). Compared to weaker Brønsted acids, the superacid consistently provides better yields along with reduced reaction times and it eliminates the need for heating. The superacid is particularly effective when dicationic electrophilic intermediates are generated in the conversions, for example with the diazaspirocycle syntheses.

Double Addition Reactions Involving Vinyl-Substituted N-Heterocycles and Active Methylene Compounds.

A series of conjugate addition reactions have been performed with vinyl-substituted N-heterocycles in acid-catalyzed conversions. Using active methylene compounds, double conjugate addition reactions have been accomplished to provide dipyridyl and related heterocyclic products. These conversions have utilized 1,3-dicarbonyl compounds, cyano esters, a cyano sulfone, and malonyl nitrile as nucleophiles. The Michael accepting groups include vinyl-substituted pyridines, quinoline, and pyrazine. Double conjugate addition reactions have also been accomplished with 2,6-divinylpyridine and related systems.