Tert-butyl-substituted tripyrranes: insights into the steric and conformational factors that influence porphyrinoid ring formation in the "3 + 1" methodology.
The MacDonald "3 + 1" route for porphyrinoid synthesis involves the acid-catalyzed condensation of tripyrranes with monocyclic dialdehydes, followed by an oxidation step. In the present study, yields were found to be greatly diminished when tert-butyl substituents were introduced on to the tripyrrane unit. Analysis of the proton NMR spectra for the tripyrranes indicates that the preferred conformation in solution has been radically altered by the presence of these tert-butyl moieties. This appears to be the first time that the NMR properties of an intermediate in porphyrin or porphyrin analogue synthesis have been correlated to its effectiveness in macrocycle formation.
Department of Chemistry, Illinois State University, Normal 61790-4160, USA.
Wenhua
W
Jiao
Timothy D
TD
Lash