Light-Induced Geometric Isomerization of 1,2-Diphenylcyclopropanes Included within Y Zeolites:  Role of Cation−Guest Binding

Abstract

Through a systematic study of several diphenylcyclopropane derivatives, we have inferred that the cations present within a zeolite control the excited-state chemistry of these systems. In the parent 1,2-diphenylcylopropane, the cation binds to the two phenyl rings in a sandwich-type arrangement, and such a mode of binding prevents cis-to-trans isomerization. Once an ester or amide group is introduced into the system (derivatives of 2beta,3beta-diphenylcyclopropane-1alpha-carboxylic acid), the cation binds to the carbonyl group present in these chromophores and such a binding has no influence on the cis-trans isomerization process. Cation-reactant structures computed at density functional theory level have been very valuable in rationalizing the observed photochemical behavior of diphenylcyclopropane derivatives included in zeolites. While the parent system, 1,2-diphenylcylopropane, has been extensively investigated in the context of chiral induction in solution, owing to its failure to isomerize from cis to trans, the same could not be investigated in zeolites. However, esters of 2beta,3beta-diphenylcyclopropane-1alpha-carboxylic acid could be studied within zeolites in the context of chiral induction. Chiral induction as high 20% ee and 55% de has been obtained with selected systems. These numbers, although low, are much higher than what has been obtained in solution with the same system or with the parent system by other investigators (maximum approximately 10% ee).

Catalytic Supramolecular Photochirogenesis

“…[49] Triplet-sensitized photoisomerization of 27a adsorbed in 4-methoxyacetophenone-immobilized NaY zeolite affords 28a/29a in up to 55% de, which is much higher than that obtained in solution phase (≤5% de). [50] Benzonorbornadiene 30 is photochemically inert upon direct irradiation, but smoothly undergoes the di-pmethane rearrangement to 31 upon triplet sensitization (Scheme 8). [51,52] The use of TlY zeolite as a host accelerates the intersystem crossing of singlet-excited photosubstrate due to the heavy atom effect, facilitating the rearrangement to 31 via the triplet excited state.…”

Supramolecular Photochirogenesis

“…The stereochemical outcomes of the sensitized photoisomerization considerably differ from those of the direct irradiation. 53 Photoirradiation of steroids 20 (Scheme 4.9 ) affords reduction products 21 and 22 , respectively, through α -and β -face addition. Although irradiations of 20 in hexane, high -silica Y zeolite, or MCM -41 mesoporous silica give no reduction product, photolysis of 20 in 2 -propanol yields the less -hindered α -face addition to give 22a in 73% yield and 22b in 65% yield.…”

“…By using ephedrine as a chiral inductor, a highest ee of 20% has been reported for 28c . 53,67 Enantiodifferentiating photocyclization of tropolone derivatives 29 (Scheme 4.13 ) to chiral bicycloheptadienones 30 has been considerably investigated in the solid state. 76 -81 Ramamurthy and coworkers studied the photocyclization using zeolites chirally modifi ed with norephedrine, ephedrine, or pseudo- 82,83 Chiral photoproduct 30c was obtained in 69% ee by using ephedrine -modifi ed zeolite.…”

Controlling Photoreactions Through Noncovalent Interactions Within Zeolite Nanocages

“…The photobehavior of the amides of 2,3 -diphenylcyclopropane -1 -carboxylic acid ( 34 / 35b and 34 / 35c ; Scheme 10.9 ) is consistent with this expectation. 33 For example, the alkyl amides of 2,3 -diphenylcyclopropane -1 -carboxylic acid upon triplet sensitization within NaY gave both trans and cis isomers similar to that in solution (Scheme 10.9 ). Computational (B3LYP/6 -31G * ) results on methyl amide of 2,3 -diphenylcyclopropane -1 -carboxylic acid provide an insight into the excitedstate behavior of the above molecules.…”