Extensive effort has been expended to utilize π-allyl palladium-complexes as electrophilic allyl donor intermediates in cooperative dual catalysis, but their counter anions such as carboxylates or alkoxides are almost always discarded as waste. We have developed a cooperative Pd(0)/Rh(II) dual catalysis system that utilizes both the electrophilic allyl and nucleophilic counter anion functionalities inherent in the starting allylic substrates. In this cooperative catalysis, redox compatible Pd(0) and Rh(II) catalysts selectively activate allylic substrates and N-sulfonyl-1,2,3-triazoles to generate π-allyl Pd(II)-complexes and 1,3-ambivalent equivalent aimino Rh(II)-carbenoid intermediates, respectively. The counter anion of the π-allyl Pd(II)-complex acts as a nucleophile transferring to the electrophilic carbenic carbon to form Pd/Rh-associated zwitterionic intermediates, in which the cationic palladium species may coordinate with both counter anion and imine nitrogen in the same plane establishing the (Z)-geometry of the products.
A silica monolithic column chemically modified with L-pipecolic acid as chiral stationary phase has been developed for chiral separation of dansyl amino acids by capillary electrochromatography-mass spectrometry (CEC-MS). The monolithic column was prepared by a sol-gel process and subsequent chemical modification by L-pipecolic acid as chiral selector with 3-glycidoxypropyltrimethoxysilane as spacer. Interestingly, it was found that the L-pipecolic acid-modified monolithic column can hold copper(II) ions tightly after loading Cu(II) ions during column preparation and conditioning and allows CEC separation to be conducted based on chiral ligand exchange with MS detection by a mobile phase without copper ions. It has been demonstrated that the chiral monolithic column operates well for enantioseparation of several dansyl amino acids by CEC-MS.
A straightforward route toward construction of α-quaternary chiral β-lactam moiety via Rh(II)/Pd(0)catalyzed stereoselective relay catalytic reaction is reported. This asymmetric dual relay catalysis involves Rh(II)-catalyzed enantioselective intramoluecular C−H insertions of αdiazoamides, and sequential Pd(0)-catalyzed diastereoselective intermolecular allylic alkylation. Under mild reaction conditions, a broad range of α-quaternary allylated chiral βlactams have been synthesized in high yields (up to 99%) with excellent stereoselectivities [up to diastereomeric ratio (dr) >99:1, up to 98% enantiomeric excess (ee)].
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.