Stereoselectivity in Ene Reactions with ¹O₂: Matrix Effects in Polymer Supports, Photo‐oxygenation of Organic Salts and Asymmetric Synthesis

Abstract

The ene reaction of chiral allylic alcohols is applied as a tool for the investigation of intrapolymer effects by means of the stereoselectivity of the singlet-oxygen addition. The diastereo selectivity strongly depends on the structure of the polymer, the substrate loading degree and also on the degree of conversion demonstrating additional supramolecular effects evolving during the reaction. The efficiency and the stability of polymer-bound sensitizers were evaluated by the ene reaction of singlet oxygen with citronellol. The ene reaction with chiral ammonium salts of tiglic acid was conducted under solution phase conditions or in polystyrene beads under chiral contact ion-pair conditions. The products thus obtained precipitate during the photoreaction as ammonium salts. Moderate asymmetric induction was observed for this procedure for the first time.

Enantio‐ and Diastereoselective Synthesis of exo‐Peroxyacetals: An Organocatalyzed Peroxyhemiacetalization/oxa‐Michael Addition Cascade

“…[1][2][3][4][5] However,t odate, the corresponding catalytic enantioselective strategies for the synthesis of chiral peroxides are less explored. [6][7][8][9] Moreover,asper our knowledge,there is still ascarcity of methods for the catalytic enantio-and diastereoselective synthesis of peroxides.…”

Efficient Solar Photooxygenation with Supported Porphyrins as Catalysts

“…This fact points to another possible explanation of this solvent effect, which is related to the solvation process and the greater or smaller amount of solvent molecules that are present at the polymer surface where the oxidative process occurs. This solvation process has been implicated in the observed diastereoselectivities of ene reactions with supported catalysts21 and may also be active in this case. However, the most important difference with the CHCl 3 system is that, with EtOH, almost no p ‐cymene is formed.…”

Concepts of Stereoselective Photochemistry and a Case Study: the Paterno-Buchi Reaction

“…This type of behaviour was observed in the Paternò-Büchi reaction (se below) and in the ene-reaction of allylic alcohols with singlet oxygen. In particular, in the reaction between allylic alcohols and singlet oxygen gave the preferential formation of the syn isomer (Scheme 11) [33][34][35][36] and this reaction has been used in the synthesis of artesiminin like antimalarial products [37][38][39][40][41]. …”