Chemo, regio, and stereoselective photo-oxygenations: Conformational and substituent effects, biomass valorization, and applications in photomicroreactors

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This project deals with the development of new substrate classes, reaction conditions, microreactor setups, and follow-up reactions of photooxygenation processes with singlet oxygen. We wish to study the effects of conformational control on the reactivity and selectivity of cyclohexene derivatives in Schenck-ene oxidations. A combined synthetic, theoretical, and operational effort will introduce new anellated cyclohexenes that engage in highly selective dioxygenation under mild conditions. Mechanistic studies will be devoted to substituent effects in bicyclic alkenes and cycloalkenylarenes to elucidate conformational strain and mechanistic dichotomies. Various follow-up reactions of the resultant allylic hydroperoxides will be studied in the presence of reductants, oxidants, catalysts, and nucleophiles to access a wide chemical space of oxygenated platform molecules. Continuous photo-oxidations with air/oxygen offer largely untapped potential for the valorization of biomass chemicals. We will demonstrate this concept in a combined technical, analytical, and mechanistic study with cardanol mixtures from cashew nutshell waste. Reactions between the three distinct "phases" liquid, gas, and light generally suffer from low dispersion (mixing, light attenuation). We will therefore continue our ongoing efforts to design and construct new modular photoreactors for applications to photooxygenations with oxygen/air with residence times in the few min range.