Intramolecular Hydrogen Atom Transfer Reactions (HAT) promoted by photochemical excited carbonyls
This research line started 10 years ago and is focused on the study of HAT reactions promoted by photochemically excited carbonyls. Within this type of reaction, 1,2-diketones are an unique case because they not only are activated under ultraviolet irradiation, but also with visible light.
As a result of our research we have developed two new synthetic methodologies based on photochemical reactions of 1,2-diketone systems in carbohydrates, promoted simply by visible light irradiation.
The Norrish-Yang photocyclization of deco-2,3-diuloses, initiated by a 1,5-HAT reaction trough the external carbonyl group (in red) and followed by an oxidative cleavage of the obtained spirocycle, allow the stereocontrolled synthesis of C-ketosides, very useful as chiral synthons.
On the other hand, a sequential process of Norrish II-photoelimination-aldol cyclization, triggered by a 1,5-HAT reaction through the internal carbonyl group (in blue), leads to the contraction of the six-membered ring of nono-2,3-diuloses allowing the synthesis of trans-dialkylated cyclopentitols, glycomimetics of great interest as potencial glycosidase inhibitors.
The ring contraction reactions of hexopyranose sugars that provide in a single synthetic process enantiomerically pure polyfunctional cyclopentanes, constitute a highly effective biomimetic approach to the synthesis of natural cyclopentanoids. The cyclopentane subunits of trehazoline, calditol and bacteriohopanoids are particularly accessible with our methodology.
We are currently working on unraveling the mechanical aspects of these processes as well as extending this study to other 1,2-dicarbonyl systems.
Elisa Isabel De León Alonso
