Dirhodium -catalyzed

Predict the structure of product (8) for the following dirhodium-catalyzed... 

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). 

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%... 

Komecki KP, Berry JF. Evidence for a one-electron mechanistic regime in dirhodium-catalyzed intermoleciflar C-H amination. Chem EurJ. 2011 17 5827-5832. 

Zhang X, Xu H, Zhao C. Mechanistic investigation of dirhodium-catalyzed intramolecular aHylic C-H amination versns alkene azitidination reactions. J Org Chem. 2014 79 9799-9811. 

Liu W-J, Chen Z-L, Chen Z-Y, Hu W-H. Dirhodium catalyzed intramolecular enantioselective C—H insertion reaction of A-cumyl-A-(2-/)-anisylethyl)diazoacetamide synthesis of (—)-rolipram. Tetrahedron Asymm. 2005 16 1693-1698. 

One of the most dramatic recent developments in metal carbene chemistry catalyzed by dirhodium(II) has been demonstration of the feasibility and usefulness of intermolecular carbon-hydrogen insertion reactions [38, 91]. These were made possible by recognition of the unusual reactivity and selectivity of aryl- and vinyldiazoacetates [12] and the high level of electronic control that is possible in their reactions. Some of the products that have been formed in these reactions, and their selectivities with catalysis by Rh2(S-DOSP)4, are reported in Scheme 10. 

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... 

Asymmetric synthesis of the rocaglamides was accomplished by employing [3+2] photo-cycloaddition mediated by functionalized TADDOL based chiral Brpnsted acids. The synthesis consisted of a [3+2] dipolar cycloaddition, a base-mediated a-ketol rearrangement and a hydroxyl-directed reaction <06JA7754>. Asymmetric synthesis of 1,2-dihydrobenzo /j]furans was achieved by adamantylglycine derived dirhodium tetracarboxylate catalyzed C-H insertion <06OL3437>. 

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. 

The dirhodium(n)-catalyzed asymmetric C-H insertion has been recognized as a powerful procedure for the preparation of many interesting compounds.35,43,68,179 Doyle et al. developed an efficient procedure for the enantio-selective syntheses of lactams. - The acyclic terminal diazoacetamides gave moderate enantioselectivity... 

Dirhodium(II) carboxylate catalysts have been used extensively for the catalysis of carbene insertions. In many cases, impressive selectivities have been achieved (19-21). In an effort to find selective catalysts for carbenoid insertions, Moody screened a series of dirhodium(II) carboxylate catalysts for their ability to catalyze carbenoid Si-H insertion (22). The authors surveyed the commercially available carboxylic acids, -10,000 of which are chiral. The members of this group that contained functionality that is incompatible to the reaction were culled out. The remaining chiral carboxylic acids (-2000 compounds) were then grouped into 80 different clusters. There is no discussion presented for the criteria used in the grouping of the acids. A representative acid from each cluster was then chosen for... 

R,5S)-(-)-6,6-Dimethyl-3-oxabicyclo[3.1,0]hexan-2-one. Highly tnantioselective Intramolecular Cyclopropanation Catalyzed by Dirhodium(ll) Tetrakis[methyl 2-pyrrolidone-5(R)-carboxylate],... 

The metal-catalyzed decomposition of diazo compounds has broad applications in organic synthesis [1-8]. Transient metal carbenoids provide important reactive intermediates that are capable of a wide variety of useful transformations, in which the catalyst dramatically influences the product distribution [5]. Indeed, the whole field of diazo compound decomposition was revolutionized in the early 1970s with the discovery that dirhodium tetracarboxylates 1 are effective catalysts for this process [9]. Many of the reactions that were previously low-yielding using conventional copper catalysts were found to proceed with unparalleled efficiency using this particular rhodium catalysis. The field has progressed extensively and there are some excellent reviews describing the breadth of this chemistry [5, 7, 10-17]. 

In contrast to the intermolecular cyclopropanation, the dirhodium tetraprolinates give modest enantioselectivities for the corresponding intramolecular reactions with the do-nor/acceptor carbenoids [68]. For example, the Rh2(S-DOSP)4-catalyzed reaction with al-lyl vinyldiazoacetate 32 gives the fused cyclopropane 33 in 72% yield with 72% enantiomeric excess (Eq. 4) [68]. The level of asymmetric induction is dependent upon the substitution pattern of the alkene cis-alkenes and internally substituted alkenes afford the highest asymmetric induction. Other rhodium and copper catalysts have been evaluated for reactions with vinyldiazoacetates, but very few have found broad utility [42]. 

Cyclopropenation reactions are also effectively catalyzed by dirhodium(II) compounds, and high enantiocontrol has been achieved with the Rh2(MEPY)4 catalysts (Scheme 15.3) [47]. A striking example of the catalyst effect on selectivity is found in the behavior of substrate 25 toward Rh2(5S-MEPY)4 and the more reactive Rh2(4S-IBAZ)4 (Eq. 10) [48]. With the less reactive Rh2(5S-MEPY)4 it preferentially undergoes allyhc cyclopropanation with high chemoselectivity and enantiocontrol. With the more reactive Rh2(4S-IBAZ)4 addition to the carbon-carbon triple bond is favored even though this involves construction of a ten-membered ring. 

Intermolecular amination experiments described by Muller using 02NC,5H4S02N=IPh (NsN=IPh) as the nitrene source underscore the value of certain rhodium(II) catalysts for C-H insertion (Scheme 17.5) [12, 34—36]. In accord with Breslow s finding, dirhodium carboxylates were demonstrated to catalyze the amination of allylic, benzylic, and adamantyl substrates. Notably, structurally related tetracarboxamide dimers fail to give... 

The predicted low enantiocontrol from reactions performed with methallyl diazoacetate (Eq. 5.18) was borne out in reactions catalyzed by Rh2(MEPY)4 and Rh2(MEOX)4, but when chiral imidazolidinone-ligated dirhodium(II) was used, enantioselectivity rose to 89% ee (Table 5.8) [89]. The use of CuPF6/7b also caused relatively high enantiocontrol (87% ee) [92] which, however, decreases to 82% ee when the methyl group of 36 was replaced by n-butyl, whereas with Rh2(4S-MPPIM)4 the enantiopurity of the product corresponding to 37 was 93% ee. The A-3-phenylpropanoyl substituents of Rh2(4S-MPPIM)4 help to create a more conformationally restrictive environment that leads to enhanced enantiocontrol. 

For the transition-metal catalyzed decomposition of silyl-substituted diazoacetates 205 [silyl = SiMe3, SiEt3, SiMeiBu-i, SitPr-i SiPtnBiW, SiMe2SiMe3], copper triflate and dirhodium tetrakis(perfluorobutyrate) proved to be the best catalysts114. While these two catalysts induce the elimination of N2 at 20 °C even with bulky silyl substituents, dirhodium-tetraacetate even at 100 °C decomposes only the trimethylsilyl-and triethylsilyl-diazoacetates. When the decomposition reactions are carried out in... 

Molecular mechanics was also used to model enantioselective metal-carbene transformations catalyzed by chiral dirhodium(II) compounds155. Here, a considerably more thorough approach was used, and the experimental structures of the catalysts were accurately reproduced. A difficulty encountered in this study was the parameterization of the metal-carbene intermediate. This might be part of the reason why in some cases the predicted enantioselectivities were opposite to those observed 55. ... 

Alkyl migration, aluminum-mediated, 3, 279 Alkylphosphines, in Rh-catalyzed hydroformylations dirhodium tetraphosphine, 7, 252 monophosphines, 7, 252 Alkylsilanes... 

The cyclic /J-dicarbonyl iodonium ylides can undergo [3 + 2] cycloaddition reactions with various substrates under catalytic or photochemical conditions, presumably via a stepwise mechanism [153-156]. In a recent example, iodonium ylide 211, derived from dimedone, undergoes dirhodium(II) catalyzed thermal [3+ 2]-cycloaddition with acetylenes 212 to form the corresponding furans 213 (Scheme 75). Under photochemical conditions ylide 211 reacts with various alkenes 214 to form dihydrofuran derivatives 215 [156]. 

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