title: Enhanced enantio- and diastereoselectivity via confinement and cation binding: yang photocyclization of 2-benzoyladamantane derivatives within zeolites.
abstract: Irradiation of 2-benzoyladamantane derivatives in zeolites yields the endo-cyclobutanols as the only photoproduct via a gamma-hydrogen abstraction process. The cyclobutanols readily undergo retro-aldol reaction to give delta-ketoesters. The enantiomeric excess (ee) in the endo-cyclobutanols is measured by monitoring the ee in the ketoesters. Whereas in solution the ee in the product ketoester is zero, within achiral NaY zeolite, in the presence of a chiral inductor such as pseudoephedrine, ee's up to 28% have been obtained. The influence of zeolite on several chiral esters of 2-benzoyladamantane-2-carboxylic acids has also been examined. Whereas in solution the diastereomeric excess is <15%, in zeolite the delta-ketoesters are obtained in 79% de (best examples). Ab initio computations suggest that enhancement of chiral induction within zeolites is likely to be due to cation complexation with the reactant ketone. Alkali ion-organic interaction, a powerful tool, is waiting to be fully exploited in photochemical and thermal reactions. In this context zeolites could be a useful medium as one could view them as a reservoir of "naked" alkali ions that are only partially coordinated to the zeolite walls.
authors.affiliation: Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, USA.
authors.forename: Arunkumar
authors.initials: A
authors.lastname: Natarajan
authors.forename: Abraham
authors.initials: A
authors.lastname: Joy
authors.forename: Lakshmi S
authors.initials: LS
authors.lastname: Kaanumalle
authors.forename: John R
authors.initials: JR
authors.lastname: Scheffer
authors.forename: V
authors.initials: V
authors.lastname: Ramamurthy