1. Stereochemical Studies of Fluorescent Tröger’s Bases
David E. Lewis, Department of Chemistry, University of Wisconsin-Eau Claire, Eau Claire, WI 54702
The Tröger’s base skeleton is a rigid framework containing two chiral nitrogen atoms at bridgehead positions. Under acid catalysis, the ring system undergoes inversion, but two mechanisms for the inversion have been proposed Our primary goal is to use symmetrically substituted chiral Tröger’s bases to probe the mechanism of this ring inversion. The synthesis of the required chiral compounds will require the synthesis of the optically pure 4-amino-3-(1-hydroxyethyl)-N-alkyl-1,8-naphthal-imides, and then condensing them. The synthesis of the required alcohols continues to be problematic.
Attempts to incorporate a carbon substituent at C-3
During attempts to improve the yield of the Henry reaction by displacing a nitro group with the nitromethane anion, we found that the 3-nitro-4-alkylamino-1,8-naphthalimides are unusually acidic, and that the nitro compound itself is subject to restricted rotation around the C—N bond. Our attempts to resolve the two atropisomers have so far yielded ambiguous results. If we can resolve these atropisomers, this would be the first case of stable atropisomers that do not possess a biaryl skeleton.
Substitution of the halogen in the 3-bromo-4-alkylamino-1,8-naphthalimides has been accomplished by Ullmann-type displacement with excess cuprous cyanide in refluxing DMF, and by a photochemical Henry-type reaction in nitromethane. The yields are modest for both reactions. Our attempts at coupling the bromide with an alkynide anion in DMF in the presence or absence of a palladium catalyst have failed: in the absence of a heterogeneous palladium (0) catalyst, reduction of the halide occurs; in the presence of the catalyst, no reaction occurs at all.