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- Title
Sequential Norrish Type II Photoelimination and Intramolecular Aldol Cyclization of α-Diketones: Synthesis of Polyhydroxylated Cyclopentitols by Ring Contraction of Hexopyranose Carbohydrate Derivatives.
- Authors
Alvarez‐Dorta, Dimitri; León, Elisa I.; Kennedy, Alan R.; Martín, Angeles; Pérez‐Martín, Inés; Riesco‐Fagundo, Concepción; Suárez, Ernesto
- Abstract
The excitation of the innermost carbonyl of nono-2,3-diulose derivatives by irradiation with visible-light initiates a sequential Norrish type II photoelimination and aldol cyclization process that finally gives polyfunctionalized cyclopentitols. The rearrangement has been confirmed by the isolation of stable acyclic photoenol intermediates that can be independently cyclized by a thermal 5-(enol exo)- exo- trig uncatalyzed aldol reaction with high diastereoselectivity. In this last step, the large deuterium kinetic isotope effect found for the 1,5-hydrogen atom transfer seems to indicate that the aldol reaction runs through a concerted pericyclic mechanism. Owing to the ready availability of pyranose sugars of various configurations, this protocol has been used to study the influence of pyranose ring-substituents on the diastereoselectivity of the aldol cyclization reaction. In contrast with other pyranose ring contraction methodologies no transition-metal reagents are needed and the sequential rearrangement occurs simply by using visible light and moderate heating (0 to 60 °C).
- Subjects
ALDOLS; RING formation (Chemistry); POLYPHENOLS; CHEMICAL reactions; PYRANOSES; CARBONYL compounds; SUGAR derivatives
- Publication
Chemistry - A European Journal, 2013, Vol 19, Issue 31, p10312
- ISSN
0947-6539
- Publication type
Article
- DOI
10.1002/chem.201301230