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Notable substituent and temperature effects on the regioselectivity and the efficiency in Paternò-Büchi reaction of 4,4′-disubstituted benzophenones with 1,3-dimethyluracil and 1,3-dimethylthymine

Paper ID Volume ID Publish Year Pages File Format Full-Text
28458 44075 2006 7 PDF Available
Title
Notable substituent and temperature effects on the regioselectivity and the efficiency in Paternò-Büchi reaction of 4,4′-disubstituted benzophenones with 1,3-dimethyluracil and 1,3-dimethylthymine
Abstract

The photochemical [2 + 2] cycloadditions (the so-called Paternò-Büchi (PB) reaction) of 1,3-dimethyluracil (DMU) and 1,3-dimethylthymine (DMT) with benzophenone (1d) and its derivatives (BPs) with 4,4′-disubstituted groups including CH3O (1a), CH3 (1b), t-Bu (1c), F (1e), Cl (1f) and CN (1g) generate two series of regioisomeric oxetanes, A and B, and reveal notable substituent effects on the regioselectivity (A:B) and the photochemical efficiency, that is a higher ratio of A:B and lower efficiency for the BPs with electron-donating groups (EDGs), and a contrary effect for the BPs with electron-withdrawing groups (EWGs), such as A:B ≥ 95:5 for 1a to 32:68 for 1g in DMU photochemical system. The PB reactions of DMU with three BPs (1d, 1e and 1g) were performed at various temperatures, and temperature effects on the regioselectivity and the efficiency were observed. The ratio of photoproducts (A:B) in the DMU systems decreases with increasing the reaction temperature, such as DMU–1d system, ranging from 75:25 at −30 °C to 55:45 at 60 °C. On the basis of computational studies, the substituent effects were relationalized in terms of stability and charge distribution of intermediary triplet diradicals. The EWGs can stablize triplet diradicals especially the diradicals causing oxetanes B, and a destablization for EDGs. It was demonstrated that temperature effects originate from the conformational properties of intermediatary triplet diradicals.

Keywords
Paternò-Büchi reaction; Regioselectivity; DNA base; Benzophenones; Substituent effect; Temperature effect; Conformational analysis; Diradicals
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Notable substituent and temperature effects on the regioselectivity and the efficiency in Paternò-Büchi reaction of 4,4′-disubstituted benzophenones with 1,3-dimethyluracil and 1,3-dimethylthymine
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 183, Issues 1–2, 30 September 2006, Pages 198–204
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us