OP-II-3

PP-II-27EFFICIENT OXYGENATION OF ALLYLIC COMPOUNDS BY SINGLETOXYGEN IN MICROSTRUCTURED REACTORSLoponov K. 1 , Malkov A. 2 , Lapkin A. 11 School of Engineering, University of Warwick, k.n.loponov@warwick.ac.uk2 Department of Chemistry, Loughborough UniversityOxyfunctionalization of allylic substrates by singlet oxygen ( 1 O 2 ) is a highlyversatile synthetic method. For example, terpene-derived chiral ligands proved to besuccessful in a number of metal-based and metal-free catalytic transformations [1].The key step for the synthesis of these catalysts is 1 O 2 mediated conversion of α-pinene to pinocarvone. Another example is stereoselective photooxygenation ofaromatic chiral homoallylic alcohols (ACHA), which may be further employed in thesyntheses of important natural products, such as antibiotic showdomycin, or natural(pseudouridine) and artificial nucleobases.The most frequently used method of 1 O 2 generation in solution is photosensitizedenergy transfer from the photo-excited states of dissolved organic dye molecules toO 2 . The process involves bubbling oxygen through the illuminated reaction mixture ina batch photoreactor and requires up to two days for completion on a several gramsscale. Scaling up this protocol is limited by the available equipment due to inefficientlight utilisation and hazards associated with unattended use of O 2 . Moreover, in mostcases the sensitizers are not reusable due to the complexity of separating them fromthe homogeneous reaction mixture. Microstructured reactors with the unique featuresof microchannels such as short molecular diffusion distances, excellent heat-transfercharacteristics, and large surface-to-volume ratios, allow safe exploitation ofexplosive processes [2]. Better light penetration through the entire microchanneldepth and spatial uniformity of illumination of the reaction medium provide moreefficient light utilisation. Furthermore, once optimized, the process can be easilyscaled up by the ‘numbering up’ of the microreactor units. In addition, problemsrelated to recycling of the sensitizers can be overcome by immobilisation of dyes onthe surface of microchannels.Our work is aimed at developing the scalable microstructured reactor unit forefficient 1 O 2 mediated oxyfunctionalization of allylic compounds useful for thesynthesis of important chemicals.In our study we tested anodically bonded glass-to-silicon flat microstructuredreactor with meandering reaction channel attached to metal plate heat exchanger inthe oxygenation of α-pinene by 1 O 2 (Figure 1). We used continuous and recirculating382