Asymmetric induction during electron transfer mediated photoreduction of carbonyl compounds: role of zeolites

Shailaja, J.; Kaanumalle, Lakshmi S.; Sivasubramanian, Karthikeyan; Natarajan, Arunkumar; Ponchot, Keith J.; Pradhan, Ajit; Ramamurthy, V.

doi:10.1039/b517069a

Cited by 10 publications

(4 citation statements)

References 14 publications

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“…Our computational and solidstate NMR results in the case of phenyl cyclohexyl ketones were recently presented. 33 In this example, we showed that the alkali ion enforces an interaction between the chiral inductor and the ketone. We believe that the same phenomenon plays a role in aoxoamides as well.…”

Section: Discussionmentioning

confidence: 86%

“…During the last decade, we have provided several examples in which enantioand diastereoselectivities were obtained in zeolites but not in solution. [32][33][34][35][36][37][38][39] Recognizing the lack of availability of chiral zeolites, we have modified the interior of an achiral zeolite by adsorbing optically pure chiral inductors. In another approach, we employed covalently linked chiral auxiliaries to bring about chiral induction in photoreactions.…”

Section: Introductionmentioning

confidence: 99%

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Asymmetric induction during photocyclization of chiral and achiral α-oxoamides within achiral zeolites

Natarajan

Ramamurthy

2006

Org. Biomol. Chem.

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The photochemistry of 31 alpha-oxoamides capable of undergoing gamma-hydrogen transfer has been examined within zeolites. These molecules, upon excitation, yield two products--a beta-lactam and oxazolidinone--in solution, both resulting from gamma-hydrogen transfer. While in benzene the major product is oxazolidinone, within an MY zeolite, the main product is a beta-lactam. In this investigation, we have focused our attention on asymmetric induction in the formation of the beta-lactam product. Two approaches--using a chiral inductor and chiral auxiliary--have been employed. While in solution, in the presence of chiral inductors, achiral alpha-oxoamides yield beta-lactams with zero enantioselectivity; within zeolites, an ee of up to 44% has been achieved. Alpha-oxoamides appended with a chiral auxiliary gave beta-lactams with less than 5% diastereoselectivity in solution while within zeolites, the same alpha-oxoamides gave the products with de's of up to 83%. Such a remarkable influence of zeolites is attributed to an alkali ion interaction with the reactant alpha-oxoamides and to the confined environment of the zeolite interior. At this stage, we have not been able to provide a model with predictive power and further work is needed to understand this valuable asymmetric induction strategy.

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Section: Discussionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Asymmetric induction during photocyclization of chiral and achiral α-oxoamides within achiral zeolites

Natarajan

Ramamurthy

2006

Org. Biomol. Chem.

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“…This choice restricts the reaction to cage A in Figure 2. To fulfill this criterion, we chose an amine-induced photoreduction of carbonyl compounds (Scheme 1) [56,57,58]. This reaction is prompted by an electron transfer from amine to an excited ketone.…”

Section: Chiral Inductor As An Active Co-guest: Photoreduction Promentioning

confidence: 99%

Achiral Zeolites as Reaction Media for Chiral Photochemistry

Ramamurthy

2019

Molecules

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Obtaining enantiomerically-enriched photoproducts from achiral reactants has been a long-sought goal. The various methods developed to achieve chiral induction in photoproducts during the last fifty years still suffer from a lack of predictability, generality, and simplicity. With the current emphasis on green chemistry, obtaining enantiomerically enriched products via photochemistry is a likely viable alternative for the future. Of the various approaches developed during the last three decades, the one pioneered in the author’s laboratory involved the use of commercially-available and inexpensive achiral zeolites as the media. This approach does not use any solvent for the reaction. Examples from these studies are highlighted in this article. Since no chiral zeolites were available, when the work was initiated in the author’s laboratory, commercially-available zeolites X and Y were modified with chiral inductors so that the reaction space becomes chiral. The results obtained established the value of chirally-modified, commercial zeolites as media for achieving chiral induction in photochemical reactions. A recent report of the synthesis of a chiral zeolite is likely to stimulate zeolite-based chiral photochemistry in synthesizing enantiomerically-pure organic molecules. The availability of chiral zeolites in future is likely to energize research in this area. Our earlier observations on this topic, we believe, would be valuable for progress of the field. Keeping this in mind, I have summarized the work carried out in our laboratory on chiral photochemistry on chirally-modified zeolites. This review does not include examples where high chiral induction has been obtained via a strategy that examines molecules appended with chiral auxiliary within achiral and chirally-modified zeolites. The latter approach yields products with diastereomeric excess >80%.

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“…The role of the cation is likely to immobilize the substrate either by cation-π interactions or by cation-dipolar interactions with nitro or carbonyl groups. Work is still ongoing to improve both the generality and predictability of asymmetric induction in zeolites [136][137][138].…”

Section: Intrazeolite Asymmetric Photoreactionsmentioning

confidence: 99%

Supramolecular photochemistry in zeolites: From catalysts to sunscreens

Chrétien

2007

Pure and Applied Chemistry

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Zeolites are nanoporous, crystalline aluminosilicate materials comprised of a series of strictly uniform channels and cavities repeating along the tri-directional structure of the lattice. Over the last 30 years, researchers have increasingly recognized the desirable properties of these materials as hosts for photochemical reactions. This review will endeavor to draw attention to the properties of zeolite materials that make them appealing substrates for hosting guest molecules during photochemical reactions. An overview of some classical examples in zeolite host-guest photochemistry will be presented along with a brief description of a new use for zeolite materials as protective encapsulators.

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Asymmetric induction during electron transfer mediated photoreduction of carbonyl compounds: role of zeolites

Cited by 10 publications

References 14 publications

Asymmetric induction during photocyclization of chiral and achiral α-oxoamides within achiral zeolites

Asymmetric induction during photocyclization of chiral and achiral α-oxoamides within achiral zeolites

Achiral Zeolites as Reaction Media for Chiral Photochemistry

Supramolecular photochemistry in zeolites: From catalysts to sunscreens

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