Role of cations and confinement in asymmetric photochemistry: enantio- and diastereo-selective photocyclization of tropolone derivatives within zeolites.
Asymmetric induction in photochemical reactions has been explored using the photochemistry of tropolones as a model. Three approaches have been examined: chiral inductor, chiral auxiliary and [chiral inductor + chiral auxiliary]. All three methods gave excellent asymmetric induction in zeolite and very little or zero induction in solution. Results presented on tropolones clearly illustrate the remarkable influence that a confined space studded with cations can have on asymmetric induction. Tropolone derivatives, upon irradiation undergo 4pi-electron electrocyclization to yield a bicyclic product and a rearranged product. Enantiomeric excess up to 68% has been achieved in the cyclized product. In systems where a chiral inductor has been covalently linked, diastereomeric excess as high as 88% has been achieved within a zeolite while the same system in solution gave 10%.
Joy
Abraham
A
Department of Chemistry, University of Miami, Coral Gables, FL 33124, USA.
Kaanumalle
Lakshmi S
LS
Ramamurthy
V
V