Photoisomerization an Access to Transition State Combinations in Thiourea-, Iminium- and Dienaminecatalysis

• Applicant: Professorin Dr. Ruth M. Gschwind
• Subject Area: Organic Molecular Chemistry - Synthesis and Characterisation
• Term: from 2014 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 245388561

Transition states and their interactions are the key to reactivities and selectivities in asymmetric catalysis. So far, exclusively theoretical calculations have given access to transition states. Recently, however, we developed the DTS-hn method (Decrypting Transition States with light). There, light is used as a mechanistic tool in asymmetric transformations of double bonds. Furthermore, DTS-hn allows for the first time to determine transition state combinations based exclusively on experimental data. The application of photoisomerization to create fingerprint pattern of transition states based on modulations in rate and ee-value was first applied to transferhydrogenations of imines with chiral phosphoric acids. In this project our structural and mechanistic studies in Organocatalysis will be combined with the DTS-hn method. Selected examples from thiourea, iminium and dienamine catalysis will be used to address two main goals. First, the applicability, selectivity und optimization of photoisomerization of double bonds in reaction intermediates shall be addressed. Second, transition state combinations in thiourea, iminium and dienamine catalysis shall be determined experimentally and their structural aspects shall be revealed by a combination of NMR data (ground states) and theoretical calculations (transition states). The new DTS-hn method will allow for additional so far unprecedented insights into the mechanisms of these catalyses and to develop criteria to understand and modulate the preferences for transition state combinations.Overall the proposed synergistic combination of photoisomerization, NMR structural analysis and theoretical calculations will enable us a) to determine the transition state combinations in Organocatalysis experimentally and to refine its mechanistic comprehension, b) to develop criteria for the design and optimization of asymmetric transformations of double bonds in general and c) to understand basic effects in the dual Photo-Organocatalysis.

• DFG Programme: Research Grants