An approach to polymer-supported triplet benzophenone photocatalysts. Application to sustainable photocatalysis of an a-diazocarbonyl compound†‡ Lourdes Pastor-P´ erez, a Carla Lloret-Fern´ andez, a Hafid Anane, b Moulay Lahcen El Idrissi Moubtassim, b Miguel Julve a and Salah-Eddine Stiriba * a Covalent immobilization of 4-hydroxybenzophenone on Merrifield resins affords new heterogeneous polymeric triplet photocatalysts. Their successful application in the intramolecular triplet-sensitized photolysis of a a-diazo b-keto ester has been achieved under sustainable criteria. Remarkably, the simple recovery and reuse for up to five sequential applications have been performed, although resulting in a slightly decreasing activity. Introduction Immobilization of organic catalytic species on polymer supports represents an important issue for modern heteroge- neous catalysis, due to the increasing demand for robust, reliable and economic preparative methods. 1 However, while research dealing with the immobilization of organic catalysts is a growing area, the xation of organic photocatalysts on polymers, as a new strategy in the heterogenous protocols, has been less addressed. 2 In fact, very few reports addressing the approach of polymer-bound organic sensitizers have been published. For instance, benzoylated polystyrene–divinylben- zene copolymer beads (Merrield resins) were prepared and applied to mediate [4 + 2] photocycloaddition reactions. 3 Similar Merrield resins-supported benzophenone (BP) were also prepared and used in [2 + 2] photocycloaddition reactions as well as in E–Z isomerization of suitable alkenes in solu- tion. 4 Ionic porphyrins attached to cationically functionalized polystyrene as photosensitizers as well as pyrylium immobi- lized on Merrield resins as electron-transfer sensitizers have also been reported. 5,6 Recently, porphyrin-loaded polystyrene beads as solid support have been described and applied for ene- and [4 + 2]-cycloaddition reactions involving singlet oxygen ( 1 D g ). 7 The organic photocatalyst responsible for the sensitization of the substrates undergoing reaction oen is decomposed or transformed into new organic products. The combination of light as reagent and a polymer-covalently loaded with pho- tocatalytic species, with the possibility of recovering and reusing them, is therefore a convenient approach towards sustainable photochemistry, particularly for those catalyze- organic reactions that make use of noble transition metal complexes. 8 a-Diazocarbonyl compounds constitute a special type of organic compounds with a remarkable exibility in organic synthesis, being also key intermediates in the preparation of various pharmaceutical and naturally occurring products. 9 Their most relevant reactions are those that proceed thermally, photochemically, or catalytically with the loss of nitrogen, leading to highly reactive carbene or carbenoid species. 10 These intermediates react via a number of mechanisms, including intra- or intermolecular cyclopropanation, insertion into unac- tivated C–H and Wolff rearrangement to form new carbon– carbon bonds. 11 While the Wolff rearrangement is the major process induced by direct photolysis or thermolysis of a-diazocarbonyls that proceeds in the singlet state accompanying or following the loss of N 2 , cyclopropanation is the major process of the sensitized photolysis in solution. 12 The cyclopropanation reaction proceeds via the triplet carbene intermediate in the presence of stoichiometric amounts of the triplet sensitizer, such as benzophenone undergoing intramolecular addition to the double bond to afford the cyclopropanation product in quan- titative yields. 13 However, this approach is solvent-dependent and suffers from products stability as well as from the decom- position of the employed sensitizer. Other major drawbacks of the photolysis in solution are the recovery and separation of the sensitizers from the nal products. The covalent immobiliza- tion approach of the sensitizer on a polymer support could a Instituto de Ciencia Molecular/ICMol, Universidad de Valencia, C/. Catedr´ atico Jos´ e Beltr´ an N  2, 46980 Valencia, Spain. E-mail: stiriba@uv.es; Fax: +34 96 3543273; Tel: +34 96 3544445 b Equipe de Chimie Mol´ eculaire, Mat´ eriaux et Mod´ elisation – C3M, Facult´ e Polydisciplinaire de Sa, Universit´ e Cadi Ayyad, Sa, Morocco † Dedicated to Professor Douglass F. Taber in recognition of his outstanding contributions to the chemistry of the diazo compounds. ‡ Electronic supplementary information (ESI) available. See DOI: 10.1039/c3ra45321a Cite this: RSC Adv., 2013, 3, 25652 Received 24th September 2013 Accepted 22nd October 2013 DOI: 10.1039/c3ra45321a www.rsc.org/advances 25652 | RSC Adv., 2013, 3, 25652–25656 This journal is ª The Royal Society of Chemistry 2013 RSC Advances COMMUNICATION