The immobilization of [Rh2(S‐PTTL)(S‐TCPTTL)3] (PTTL = N‐phthaloyl‐tert‐leucinate, TCPTTL=N‐tetrachlorophthaloyl‐tert‐leucinate) has been accomplished by copolymerization of the RhII‐complex‐containing monomer with 2‐(trifluoromethyl)styrene and a flexible cross‐linker. The immobilized catalyst promoted intermolecular carbonyl ylide cycloaddition reactions in CF3C6H5 under continuous flow conditions, where high yields as well as high levels of enantioselectivity and turnover number were achieved.
The first example of enantioselective intermolecular cycloaddition of carbonyl ylides with indoles is described. The cycloaddition of five- and six-membered carbonyl ylides derived from diazodiketoesters with N-methylindoles under catalysis by dirhodium(II) tetrakis[N-tetrachlorophthaloyl-(S)-tert-leucinate], Rh(2)(S-TCPTTL)(4), gave cycloadducts in high yields and with high levels of enantioselectivity (up to 99% ee) as well as excellent exo diastereoselectivity.
Eine sehr effektive Immobilisierung von [Rh2(S‐PTTL)4] (PTTL=N‐Phthaloyl‐tert‐leucinat) gelang durch Copolymerisation des Monomers 1 mit Styrol und einem flexiblen Vernetzer. Der immobilisierte Katalysator ermöglicht die Titelreaktion bei −78 °C mit hoher Enantioselektivität und konnte für 100 Zyklen bei geringem Auswaschen (0.28 ppm) genutzt werden.
The immobilization of dirhodium(II) tetrakis[N-tetrafluorophthaloyl-(S)-tert-leucinate], [Rh 2 A C H T U N G T R E N N U N G (S-TFPTTL) 4 ], has been accomplished by copolymerization of a dirhodium(II) complex-containing monomer with styrene and 1,6-bis(4-vinylbenzyloxy)hexane as a flexible cross-linker. The polymersupported chiral fluorinated dirhodium(II) complex catalyzed the amination of silyl enol ethers with [N-(2-nitrophenylsulfonyl)imino]phenyliodinane (NsN=IPh) to provide a-amino ketones in high yields with high levels of enantioselectivity and could be used up to 20 times as the catalyst readily withstood stirring in the presence of the solid reactant.Keywords: asymmetric catalysis; heterogeneous catalysis; immobilization; nitrenes; rhodium Chiral dirhodium(II) carboxylate and carboxamidate complexes are exceptional catalysts for a wide range of enantioselective metal carbene transformations with diazocarbonyl compounds, including cyclopropanation, C À H insertion, and rearrangement or cycloaddition via ylide generation.[1] Recently, they have also been recognized as effective catalysts in metal nitrene reactions such as C À H amination and olefin aziridination. [2][3][4][5][6][7][8] Although such reactions frequently proceed in high yield and with high levels of asymmetric induction, their practical applications in pharmaceutical production are hampered by the high costs of both rhodium [9] and chiral ligands as well as the difficulty in catalyst recovery and recycling. These drawbacks have stimulated a variety of efforts toward immobilization of chiral dirhodium(II) complexes.[10-16] While considerable advances have been made in selected catalytic asymmetric carbene processes, to the best of our knowledge, there is no immobilized dirhodium(II) catalyst available for nitrene reactions. [17,18] Recently, we reported an effective immobilization of [Rh 2 A C H T U N G T R E N N U N G (S-PTTL) 4 ] (1a) [19][20][21] (Figure 1), which was achieved by preparation of a dirhodium(II) complexcontaining monomer 2a followed by copolymerization with styrene (5a) and 1,6-bis(4-vinylbenzyloxy)hexane (6) as a flexible cross-linker (Scheme 1).[22-25] The polymer-supported complex 7a with no unreacted linkers or free ligands [26] catalyzed asymmetric C À H insertions with high enantioselectivities similar to those found with the homogeneous catalyst 1a and could be used for up to 100 sequential applications with a low leaching level.[22] Very recently, a similar method proved to be beneficial for the immobilization of a chiral chlorinated dirhodium(II) complex. [27] The immobilized catalyst 7b prepared by copolymerization of dirhodium(II) complex-containing monomer 2b with 2-(trifluoromethyl)styrene (5b) and crosslinker 6 (Scheme 1) was successfully applied to intermolecular carbonyl ylide cycloaddition reactions under continuous flow conditions, where high yields as well as high levels of enantioselectivity (up to 99% ee) and turnover number (up to 11,700) were achieved.[27] Given that catalysts 7a and 7b...
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.