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.

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The synthesis of the 6-hydroxylated epimer 7 of shikimic acid from natural shikimic acid 1 is conducted by a sequence of protecting steps, dehydration to the 1,3-cyclohexadiene 4 and photosensitized singlet oxygen cycloaddition reaction. The target molecule is then obtained from the endoperoxide 9 by reduction and deprotection. A new hydroxyl group is thereby inserted into position 6 of shikimic acid whereas the configuration at position 4 is formally inverted.

Other 6-membered heterocycles R 0670A Family of New 1,2,4-Trioxanes by Photooxygenation of Allylic Alcohols in Sensitizer-Doped Polymers and Secondary Reactions. -The syntheses of several 1,2,4-trioxanes from the reaction of 1,2-hydroperoxy alcohols with aldehydes and ketones, or acetals and orthoesters are reported. The hydroperoxy alcohols are obtained by a recently published Type II photooxygenation (singlet oxygen) using polymeric sensitizer-adsorbed or covalently sensitizer-doped polymeric (macro-or nanosized) containers. The method of trans-peroxyacetalization of acetals for the synthesis of 1,2,4-trioxanes is found to be superior to the direct use of aldehydes. -(BARTOSCHEK, A.; EL-IDREESY, T. T.; GRIESBECK*, A. G.; HOEINCK, L.-O.; LEX, J.; MIARA, C.; NEUDOERFL, J. M.; Synthesis 2005, 14, 2433-2444; Inst.

Type II photooxygenation (singlet oxygen) is described as a synthetically useful way for the preparation of allylic hydroperoxides and endoperoxides using sensitizer-adsorbed or covalently sensitizer-doped polymeric (macro-or nanosized) containers. Facilitated product separation and purification as well as increased reactivity are advantages of these techniques in comparison with solution-phase photochemistry. The products generated by Type II photooxygenation have been used for the syntheses of numerous polycyclic peroxides with a common 1,2,4-trioxane core as exhibited in the natural antimalarial artemisinin.