Deprotonation of phenyl-dibenzo[b,f]tropylidene 8 with LDA/t-BuOK followed by quenching with either diastereomers of inexpensive glucose-based t-Bu-sulfinates (R)-or (S)-11 affords a sulfoxidealkene hybrid ligand as diastereomeric pairs (S S ,S C )-9 / (S S ,R C )-10 and (R S ,R C )-9 / (R S ,S C )-10, respectively, which via chromatographic/recrystallization may be separated into the four isomers. The optically pure diastereomeric ligands (S S ,S C )-9 and (S S ,R C )-10 react with [RhCl(coe) 2 ] 2 to form the dinuclear complexes (R S ,S C )-11 and (R S ,R C )-12, respectively, in which the bidentate ligands coordinate the metal centers through the sulfur and alkene donor functions. These complexes catalyze the conjugate addition of arylboronic acids to cyclic Michael acceptors with enantioselectivities of up to 99% ee. DFT calculations show the preponderant influence of planar chirality of the ligand alkene function. The enantioselectivity switch observed between (R S ,S C )-11 and (R S ,R C )-12 is explained by the inverted cis-trans coordinations of the substrate molecules in catalytic steps.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.