Dirhodium tetrakis

As shown in the previous two sections, rhodium(n) dimers are superior catalysts for metal carbene C-H insertion reactions. For nitrene C-H insertion reactions, many catalysts found to be effective for carbene transfer are also effective for these reactions. Particularly, Rh2(OAc)4 has demonstrated great effectiveness in the inter- and intramolecular nitrene C-H insertions. The exploration of enantioselective C-H amination using chiral rhodium catalysts has been reported by several groups.225,244,253-255 Hashimoto s dirhodium tetrakis[A-tetrachlorophthaloyl-(A)-/ r/-leuci-nate], Rh2(derived rhodium complex, Rh2(i -BNP)4 48,244 afforded moderate enantiomeric excess for amidation of benzylic C-H bonds with NsN=IPh. 

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],... 

Experimental Procedure 4.1.1. Preparation of an Enantiomerically Pure Rho-dium(II) Gomplex Dirhodium(II) Tetrakis[methyl 2-oxo-l-(3-phenylpr( anoyl)-4(S)-imidazolidinecarboxylate] Rh2(4S-MPPIM)4(MeCN)2 [1000]... 

Rhodium pivalate dirhodium tetrakis /i-(2,2-dimethylpropanato-0 0 )] was synthesized by heating commercially available rhodium trifluoroacetate in 8 equiv pivalic acid for 24 h followed by removal of excess acid by heating under vacuum. The cmde catalyst was purified by flash chromatogra-... 

Hashimoto has noted improved enantioselectivities for C-H insertion of indane and tetralin substrates using dirhodium tetrakis(N-phthaloyl-tert-butylleucinate)-based catalysts (Scheme 17.9) ]49]. In the best of these examples, 84% ee was obtained with 1,1-dimethyltetrahn 9 (5 equiv) and NsN=IPh. Despite the modest enantiomeric ex-... 

When the chiral catalyst tetrakis(binaphtholphosphate)dirhodium was used, moderate enantiomeric excess (50%) was obtained in cycloaddition reactions with furans and dihydrofurans (359). This method has been applied to the synthesis of several natural products that contain fused furan rings, e.g., the human platelet... 

Desymmetrization strategy in enantioselective oxonium ylide formation/[l,2]-shift reaction has been reported by Doyle and co-workers.With dirhodium(ii) tetrakis[methyl l-(3-phenylpropanoyl)-2-oxoimidazolidine-4(3 )-carboxylate] [Rh2(43 -MPPIM)4] as the catalyst, up to 88% ee is obtained (Equation (7)). 

Hodgson and co-workers have studied the intramolecular cascade carbonyl ylide formation-cycloaddition with chiral Rh(ii) catalysts.After screening a series of chiral Rh(ii) catalysts, high enantioselectivity was achieved in the reaction of 98 by using the Rh(ii) catalyst with binaphthyl phosphate-derived chiral ligands dirhodium(ii) tetrakis[(i )-6,6 -didodecylbinaphtholphosphate] [Rh2(i -DDBNP)4] (Equation (13)). 

Hashimoto and co-workers, on the other hand, studied the intramolecular reaction between cyclic carbonyl yield and dimethyl acetylenedicarboxylate (DMAD) (Equation (14)). With dirhodium(ii) tetrakis[A-benzene-fused phthaloyl-(A)-valinate] [Rh2(WBPTV)4] 104, high enantioselectivity (68-92% ee) was achieved over a range of diazo substrates.The high level of enantiocontrol provided conclusive evidence that chiral Rh(ii) catalyst is associated with the ylide in the cycloaddition step. 

Dimethylthexylsilyl trifluoromethane-sulfonate, 74 Diphenylsilane, 153 Diphenylsilane-Di- x-chlorobis(l,5-cyclooctadiene)dirhodium, 153 Diphenylsilane-Palladium(II) chloride-Triphenylphosphine, 126 Diphenylsilane-Tetrakis(triphenyl-phosphine)palladium(0)-Zinc chloride, 126... 

Rh(II) carboxylates, especially Rh2(OAc)4> have emerged as the most generally effective catalysts for metal carbene transformations [7-10] and thus interest continues in the design and development of dirhodium(II) complexes that possess chiral51igands. They are structurally well-defined, with D2h symmetry [51] and axial coordination sites at which carbene formation occurs in reactions with diazo compounds. With chiral dirhodium(II) carboxylates the asymmetric center is located relatively far from the carbene center in the metal carbene intermediate. The first of these to be reported with applications to cyclopropanation reactions was developed by Brunner [52], who prepared 13 chiral dirhodium(II) tetrakis(car-boxylate) derivatives (16) from enantiomerically pure carboxylic acids RlR2R3CC OOH with substituents that were varied from H, Me, and Ph to OH, NHAc, and CF3. However, reactions performed between ethyl diazoacetate and styrene yielded cyclopropane products whose enantiopurities were less than 12% ee, a situation analogous to that encountered by Nozaki [2] in the first applications of chiral Schiff base-Cu(II) catalysts. 

Doyle, Martin, Muller, and co-workers communicated exceptional enantiocontrol for intramolecular cyclopropanation of a series of allyl diazoacetates (Eq. 5.16) by using dirhodium(II) tetrakis(methyl 2-oxopyrrolidine-5-carboxylates), Rh2(MEPY)4, in either their R- or S-configurations [87], and they have fully elaborated these results in a subsequent report [88],... 

P-31 NMR was a powerful tool in studies correlating the structure of tertiary-phosphine-rhodium chloride complexes with their behavior as olefin hydrogenation catalysts. Triphenylphosphine-rhodium complex hydrogenation catalyst species (1) were studied by Tolman et al. at du Pont and Company (2). They found that tris(triphenylphosphine)rhodium(I) chloride (A) dissociates to tri-phenylphosphine and a highly reactive intermediate (B). The latter is dimerized to tetrakis(triphenylphosphine)dirhodium(I) dichloride (C). 

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... 

With dirhodium tetrakis(perfluorobutyrate) as catalyst, only ketene 209 was obtained in practically all cases, except for the trimethylsilyl (unseparated product mixture) and triisopropylsilyl cases (no decomposition by this catalyst). 

Intermolecular insertion to aryl C—H bonds is possible. The asymmetric intramolecular reaction of the a-diazo compound 354 catalysed by Rh2[(S)-PTTL]4, Rh2[(S)—PTTL]4 = dirhodium tetrakis[N-phthaloyl(S)—t—leucinate], afforded indane... 

Substituted cycloprop-2-ene-l-carboxylates isomerize in refluxing benzene in the presence of dirhodium(H)tetrakis(perfluorobutyrate) (Rh2(pbf)4) to furans, dienoates, or cyclopentyliden-acetates. This reaction has been studied in detail <95HCA129>. 

Dirhodium(II) tetrakis(carboxamides), constructed with chiral 2-pyrroli-done-5-carboxylate esters so that the two nitrogen donor atoms on each rhodium are in a cis arrangement, represent a new class of chiral catalysts with broad applicability to enantioselective metal carbene transformations. Enantiomeric excesses greater than 90% have been achieved in intramolecular cyclopropanation reactions of allyl diazoacetates. In intermolecular cyclopropanation reactions with monosubsti-tuted olefins, the cis-disubstituted cyclopropane is formed with a higher enantiomeric excess than the trans isomer, and for cyclopropenation of 1-alkynes extraordinary selectivity has been achieved. Carbon-hydro-gen insertion reactions of diazoacetate esters that result in substituted y-butyrolactones occur in high yield and with enantiomeric excess as high as 90% with the use of these catalysts. Their design affords stabilization of the intermediate metal carbene and orientation of the carbene substituents for selectivity enhancement. 

Chiral rhodium(II) carboxamides are exceptional catalysts for highly enantio-selective intermolecular cyclopropenation reactions (50). With ethyl diazoacetate and a series of alkynes, use of dirhodium(II) tetrakis[methyl 2-pyrrolidone-5-(R)-carboxylate], Rh2(5R-MEPY)4, in catalytic amounts ( 1.0 mol %) results in the formation of ethyl eyelopropene-3-earboxylates (eq 4) with enantiomeric excesses... 

When the vinyldiazoacetate 19, which can be prepared from benzaldehyde in a one-pot process,6 was treated in 2,2-dimethylbutane (DMB) with dirhodium tetrakis[(,S )-7V-(dodccylbenzcncsulfonyl)prolinate] [Rh2(S -DOSP)4] in the presence of 4-methyl or 4-trimethylsilyloxy-l,2-dihydronaphthalene (20), the product 21 was obtained with exceptionally high levels of enantio- and diastereo selectivity7 (Scheme 1.4f). 

The reaction is carried out under an inert atmosphere, using standard techniques.5 A 125-mL flask equipped with a magnetic stirring bar coated with Teflon is charged with 50 mL of methanol and di-p-chloro-tetrakis(ethylene)-dirhodium(0)6 (1.16 g 3.6 mmole). Trimethyl phosphite (5.00 g,40 mmole)is added dropwise over a period of 5 minutes. Upon completion of the addition, stirring is continued for 30 minutes until all the starting material is in solution. 

The 1 1 cocrystal of 2-amino-5-nitrothiazole with 4-aminobenzoic acid comprises two constituent molecules associated by a hydrogen-bonded graph set dimer through the carboxylic group across the N/N site of the thiazole [0-H...N, 2.614(3)A N-H...O, 2.991(3)A] [144], 2-Bromo-5-nitrothiazole [145], tetrakis (mefa-acetato)bis[2-(2-thionyl)-amino-5-nitrothiazole]-dirhodium-II-dihydrate [146], and /V-(4-melhoxyben/yl (-/WS-nilro-1,3-thia/ol-2-yl) urea [147] have been studied by X-ray analysis. 

TETRAKIS(ACETATO)DIRHODIUM(II) AND SIMILAR CARBOXYLATO COMPOUNDS... 

R,5S)-(-)-6,6-DIMETH YL-3-OXABICYCLO[3.1. OJHEXAN-2-ONE. HIGHLY ENANTIOSELECTIVE INTRAMOLECULAR CYCLOPROPANATION CATALYZED BY DIRHODIUM(II) TETRAKIS[METHYL 2-PYRROLIDONE-5(R)-CARBOXYLATE]... 

Dirhodium(ll) tetrakis[methyl 2-pyrrolidone-5(R)-oarboxylate], Rh2(5R-MEPV)4, and its enantiomer, Rh2(5S-MEPY)4, which is prepared by the same procedure, are highly enantioselective catalysts for intramolecular cyclopropanation of allylic diazoacetates (65->94% ee) and homoallylic diazoacetates (71-90% ee),7 8 intermolecular carbon-hydrogen insertion reactions of 2-alkoxyethyl diazoacetates (57-91% ee)9 and N-alkyl-N-(tert-butyl)diazoacetamides (58-73% ee),10 Intermolecular cyclopropenation ot alkynes with ethyl diazoacetate (54-69% ee) or menthyl diazoacetates (77-98% diastereomeric excess, de),11 and intermolecular cyclopropanation of alkenes with menthyl diazoacetate (60-91% de for the cis isomer, 47-65% de for the trans isomer).12 Their use in <1.0 mol % in dichloromethane solvent effects complete reaction of the diazo ester and provides the carbenoid product in 43-88% yield. The same general method used for the preparation of Rh2(5R-MEPY)4 was employed for the synthesis of their isopropyl7 and neopentyl9 ester analogs. 

Dirhodium(ll) tetrakis[methyl 2-pyrrolidone-5(R)-carboxylate Rh2(5R-MEPY)4t Rhodium, tetrakis[ x-(methyl 5-oxo-L-prolinato-N1 Os)]di-, (Rh-Rh) (12) (1324-35-65-5) Thionyl chloride (8,9) (7719-09-7)... 

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