One point binding chiral ruthenium Lewis acid catalysts: asymmetric intramolecular Diels Alder reactions and conformational studies
Half sandwich chiral electron poor one point binding ruthenium catalyst that I focused on was one of the research interests in the Kundig group. A more general aim was to apply these catalysts to new transformations, expanding the range of applications that these complexes can satisfactorily catalyze. Only one successful example of asymmetric type 2 IMDA cycloaddition was reported. The challenges arise from the facts that several inconsistencies remain in the reported structure assignment of ledol. We therefore employed the crucial intermediate for the first total synthesis of ent ledol to provide in good yield with excellent ee. The conformational studies of Ru dienophile complexes with NOESY and ROESY experiments revealed a conformationally coordinate structure with correlations between dienophile protons and Cp/Indenyl 'roof' or chiral BIPHOP F ligand protons of catalyst part. These NMR results helped to explain the ground state conformations in solution that probably correspond to the observed enantioselectivity in DA reactions.