Chirally modified zeolites as reaction media: Photochemistry of an achiral tropolone ether

Organic Letters

Volumn 2, Issue 2, 2000, Pages 119-121

  Joy, Abraham ^a   Scheffer, John R ^b   Ramamurthy, V ^a  

^a TULANE UNIVERSITY   (United States)

^b UNIVERSITY OF BRITISH COLUMBIA   (Canada)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0001458354     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol9903335     Document Type: Article

References (29)

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12. The chiral inductor (30 mg, 182 mM) was dissolved in a mixture of methylene chloride and hexane (1:4). NaY (300 mg) dried at 500°C was added to the above. The slurry was stirred for 8 h, filtered, and washed. The zeolite modified with the chiral inductor was dried under vacuum and added to 1 (4 mg, 20 mM) dissolved in methylene chloride-hexane (1:4). The slurry was stirred for 12 h, filtered, and washed. After the chiral inductor and the tropolone ether were loaded, the zeolite sample was dried under vacuum at 60°C. The resulting zeolite sample complexed with the chiral inductor and the tropolone ether was irradiated in hexane for 10 min. The products were extracted from the zeolite with diethyl ether. The chiral auxiliary was removed from the product mixture before evaluating the enantiomeric excess. In a typical run, the loading levels (number of molecules per supercage) of ephedrine and 1 within NaY were 1 and 0.1, respectively. Efforts to increase the loading level of ephedrine higher than this level resulted in exclusion of 1 from the zeolite. In all runs prior to and following irradiation, the hexane layer was checked for the absence of 1 by GC. This ensured that the photoreaction occurs on the surface of the zeolite.
13. The variation in ee with respect to the length of irradiation could be due to several factors. For example, the reaction could occur from different sites with different efficiencies. The contribution of these sites to the total ee may vary with time. As indicated in Scheme 1, as a result of seconadry photoreaction product 3 is formed from 2. As expected, longer irradiation times result in higher amounts of 3. Conversion of 2 to 3 could occur enantioselectively, resulting in a time dependence of the ee of isolated 2. Presently we have not identified the origin of the variation in ee with the length of irradiation.
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24. The sample prepared as described in ret 7 was exposed to laboratory humidity by placing it on the pan of a Mettler balance. The weight increase indicated the adsorption of water. The water-included sample did not displace the chiral inductor and 1 to the external surface. This was evident from the analysis of the hexane wash. For routine "wet" experiments, samples were prepared as in ref 7 but were not dried under vacuum, and all operations were performed on a laboratory benchtop instead of a drybox.
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