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Dirhodium -catalyzed complexes

An hDA reaction between Danishefsky s diene and nitrosubstituted aromatic aldehydes is catalyzed by dirhodium(n) complexes in up to 95% ee <2001JA5366, 2003JM093>. Similar dirhodium(n) complexes are also reported to be effective catalysts for this reaction <2004SL2425, 2004AGE2665, 2005JOC5291>. [Pg.626]

In 2012, Du Bois and Zare published details of a novel method to observe intermediates in the CH amination reactions catalyzed by dirhodium carboxylate complexes [88]. In this study, desorption electrospray ionization (DESl) was coupled to mass spectroscopy to capture transient intermediates from solution having very short lifetimes (ca. nanoseconds to microseconds). Rh2(esp)2 is a catalyst for the amination of alkanes, such as adamantane, as shown in Scheme 24. [Pg.283]

This overview will concentrate exclusively on the use of dirhodium(II) complexes as these are the most active catalysts for this transformation. The preparation of rhodium(II) carboxylate complexes was first reported in 1960 by the group of Chernyaev following the reaction of rhodium(III) chloride in refluxing formic acid. Their ability to decompose diazo compounds for the formation of a metaUocarbene was then discovered by Teyssie and coworkers a decade later. This seminal study has opened the vast domain of dirhodium(II)-catalyzed carbene additions that has proved highly successful. ° Their use in catalytic nitrene addition, though less extensively investigated, has also led to significant achievements that are summarized below with an emphasis on the latest developments made in the last 5 years. [Pg.79]

The catalytic aUylic C(sp )-H amination raises another critical issue in terms of chemoselectivity given the capacity of nitrenes to add to alkenes. The dirhodium-catalyzed intramolecular additions generally lead to mixtures of compounds for which the aziridines are the major products. Rhodium-bound nitrenes, indeed, have a great tendency to react with the r-electron rich systems. And in line with the previous observations (see Scheme 23), the ratio of products varies according to the rhodium tetracarboxylate complex (Scheme 26). [Pg.96]

The search for an efficient and versatile dirhodium-catalyzed asymmetric C(sp )-H amination reaction is an issue for which there is stiU ample room for improvement. The field was pioneered again by Muller who had designed chiral rhodium(II) complexes for inter- and intramolecular reactions, though with limited success as the ees did not exceed 66%. " With respect to the catalytic asymmetric intramolecular nitrene C(sp )—H insertion, the best results reported so far have been obtained with the rhodium(II) carboxamidate species Rh2(S-nap)4 This complex affords the corresponding cyclic sulfamates with excellent ees (ees enantiomeric excesses) of up to 99% (Scheme 32). However, the scope is limited to benzyhc substrates as, despite the excellent chemoselectivity, the ees remain below 84%... [Pg.100]

Enantioselective intramolecular and intermolecular C—H functionalization reactions with a-diazocarbonyl compounds catalyzed by chiral dirhodium (II) complexes have been shown to be usefiil for the synthesis of chiral... [Pg.668]

The results of unsymmetrical 7r-acid bidentate ligands, e.g., (81), have in the hydroformylation of ra-octenes was described. The preparation of seven such ligands was described. Thus, [Rh-(acac)(cod)]-catalyzed hydroformylation of ra-octene in the presence of a phosphinite ligand gave 94% ra-nonanal.295 A new upper-rim phosphacalix[4]arene 5,17-bis(diphenylphosphinomethyl)-25,26,27,28-tetrapropoxycalix[4]arene has been prepared. It reacted with [(cod)RhCl]2 to give a dirhodium complex that is an active catalyst for the hydroformylation of 1-octene and styrene.296 Rhodium complexes of [l-propyl-3-methylimidazolium+]2 [PhP(C6H4SO%)2] dissolved in the... [Pg.164]

Activation of a C-H bond requires a metallocarbenoid of suitable reactivity and electrophilicity.105-115 Most of the early literature on metal-catalyzed carbenoid reactions used copper complexes as the catalysts.46,116 Several chiral complexes with Ce-symmetric ligands have been explored for selective C-H insertion in the last decade.117-127 However, only a few isolated cases have been reported of impressive asymmetric induction in copper-catalyzed C-H insertion reactions.118,124 The scope of carbenoid-induced C-H insertion expanded greatly with the introduction of dirhodium complexes as catalysts. Building on initial findings from achiral catalysts, four types of chiral rhodium(n) complexes have been developed for enantioselective catalysis in C-H activation reactions. They are rhodium(n) carboxylates, rhodium(n) carboxamidates, rhodium(n) phosphates, and < // < -metallated arylphosphine rhodium(n) complexes. [Pg.182]

Chiral dirhodium complex 87 (see Section 7.04.2.4) catalyzes the diastereo- and enantioselective insertion of phenyldiazoacetate 251 into 1,2,3,6-tetrahydropyridine 252 to give predominantly the erythro 6-substituted-l,2,3,6-tetrahydropyridine 253 with high enantiomeric selectivity. The threo-isomex 254 is a minor product and was formed with much lower selectivity (Equation 24) <1999JA6509, 2001TL3149>. [Pg.207]

The use of chiral additives with a rhodium complex also leads to cyclopropanes enantioselectively. An important chiral rhodium species is Rh2(5-DOSP)4, which leads to cyclopropanes with excellent enantioselectivity in carbene cyclopro-panation reactions. Asymmetric, intramolecular cyclopropanation reactions have been reported. The copper catalyzed diazoester cyclopropanation was reported in an ionic liquid. ° It is noted that the reaction of a diazoester with a chiral dirhodium catalyst leads to p-lactones with modest enantioselectivity Phosphonate esters have been incorporated into the diazo compound... [Pg.1238]

A recent DFT study has shown that retention of configuration observed for the above reactions is in agreement with the insertion of singlet nitrene and a concerted product formation [150 is the transition state for the reaction shown in Equation (6.135)]. Du Bois and coworkers have performed detailed mechanistic investigations of the intramolecular sulfamate ester C-H amination reaction catalyzed by a dirhodium complex. Reactivity patterns, Hammett analysis, and kinetic isotope effect studies have provided support for the concerted, asynchronous transition structure 151. A similar conclusion was arrived at for an analogous intermolecular process. ... [Pg.375]

The aziridination and amidation reactions of imidoiodanes can be efficiently catalyzed by Rh(II) complexes [810-815]. Dirhodium(II) tetrakis[Al-tetrafluorophthaloyl-(S)-tcrt-leucinate], Rh2(S-TFPTTL)4, has been found to be an exceptionally efficient catalyst for enantioselective aminations of silyl enol ethers 661 with imidoiodane 662 to afford a-amido ketones 663 in high yields and with enantioselectivities of up to 95% ee (Scheme 3.265). The effectiveness of this catalytic protocol has been demonstrated by an asymmetric formal synthesis of (-)-metazocine [810]. This catalyst has also been used for the asymmetric synthesis of phenylglycine derivatives by enantioselective amidation of silylketene acetals with PhINTs [811]. [Pg.256]


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See also in sourсe #XX -- [ Pg.93 ]




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Dirhodium complexes

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