Rhodium catalytic amount

The diazo function in compound 4 can be regarded as a latent carbene. Transition metal catalyzed decomposition of a diazo keto ester, such as 4, could conceivably lead to the formation of an electron-deficient carbene (see intermediate 3) which could then insert into the proximal N-H bond. If successful, this attractive transition metal induced ring closure would accomplish the formation of the targeted carbapenem bicyclic nucleus. Support for this idea came from a model study12 in which the Merck group found that rhodi-um(n) acetate is particularly well suited as a catalyst for the carbe-noid-mediated cyclization of a diazo azetidinone closely related to 4. Indeed, when a solution of intermediate 4 in either benzene or toluene is heated to 80 °C in the presence of a catalytic amount of rhodium(n) acetate (substrate catalyst, ca. 1000 1), the processes... 

The carbenoid displacement reaction (see Section 1.4.5.2.1.4.) of the optically active acetoxy sulfide derivative 19 (or the corresponding methoxymethyl ether) with diazomalonate in the presence of a catalytic amount of rhodium acetate in refluxing benzene affords the tram-alkylation productl22. 

A solution of 1.93 g (6.91 mmol) of methyl 4-nitrobenzyl diazomalonate in 100 mL of dry benzene is added dropwise over 1 h to a refluxing solution of 1.79 (4.48 mmol) of (4S,5R/S )-4-acetoxy-l-(2-benzoyl-oxyethyl)-5-phenylthio-2-pyrrolidinone in 100 mL of dry benzene in the presence of a catalytic amount of rhodium acetate. The mixture is stirred under reflux for an additional hour after which the solvent is removed. The residue is chromatographed (silica gel, benzene/ethyl acetate 8 2) to furnish an oil yield 2.32 g (85%). 

Secondary amines can be added to certain nonactivated alkenes if palladium(II) complexes are used as catalysts The complexation lowers the electron density of the double bond, facilitating nucleophilic attack. Markovnikov orientation is observed and the addition is anti An intramolecular addition to an alkyne unit in the presence of a palladium compound, generated a tetrahydropyridine, and a related addition to an allene is known.Amines add to allenes in the presence of a catalytic amount of CuBr " or palladium compounds.Molybdenum complexes have also been used in the addition of aniline to alkenes. Reduction of nitro compounds in the presence of rhodium catalysts, in the presence of alkenes, CO and H2, leads to an amine unit adding to the alkene moiety. An intramolecular addition of an amine unit to an alkene to form a pyrrolidine was reported using a lanthanide reagent. 

Although the Ag(I)-catalyzed reaction of 46 leads exclusively to the cyclobutene isomer (47), the conversion of 46 into benzo[6]thiepin has been realized by a rhodium catalyst41). Treatment of 46 with a catalytic amount of dicarbonyl-2,4-pentanedio-natorhodium(I) in chloroform at 0 °C readily gives 57 % of 4 as pale yellow needles of... 

These authors also prepared novel epoxy-bridged cyclooxaalkanones in this process, the carbonyl group always acts as 1,3-dipolarophile, even if one employs ct,(3-unsaturated aldehydes. Thus, reaction of 6/2-16 with aliphatic or aromatic aldehydes 6/2-17 in the presence of catalytic amounts of rhodium acetate gave 6/2-18, regioselectively. With the a, 3-unsaturated aldehydes 6/2-20, only cycloadducts 6/2-21 were obtained using the diazo compound 6/2-19 as substrate (Scheme 6/2.3) [191]. 

Schmalz and coworkers [192] developed an efficient entry to the skeleton of colchicin (6/2-22) by reaction of 6/2-23 with catalytic amounts of rhodium acetate to give almost exclusively rac-6/2-25 in 62% yield via the 1,3-dipole 6/2-24. Small amounts of diastereomer 6/2-26 were also found as a side product (Scheme 6/2.4). 

In a similar way as described for the hydroformylation, the rhodium-catalyzed silaformylation can also be used in a domino process. The elementary step is the formation of an alkenyl-rhodium species by insertion of an alkyne into a Rh-Si bond (silylrhodation), which provides the trigger for a carbocyclization, followed by an insertion of CO. Thus, when Matsuda and coworkers [216] treated a solution of the 1,6-enyne 6/2-87 in benzene with the dimethylphenylsilane under CO pressure (36 kg cm"2) in the presence of catalytic amounts of Rh4(CO)12, the cyclopentane derivative 6/2-88 was obtained in 85 % yield. The procedure is not restricted to the formation of carbocycles rather, heterocycles can also be synthesized using 1,6-enynes as 6/2-89 and 6/2-90 with a heteroatom in the tether (Scheme 6/2.19). Interestingly, 6/2-91 did not lead to the domino product neither could 1,7-enynes be used as substrates, while the Thorpe-Ingold effect (geminal substitution) seems important in achieving good yields. 

Treatment of the diazo piperidone 254 with a catalytic amount of rhodium acetate afforded the hydroxyquinolizine derivative 255 through the mechanism summarized in Scheme 52 <2000JOC7124>. 

Mejla-Oneto and Padwa have explored intramolecular [3+2] cycloaddition reactions of push-pull dipoles across heteroaromatic jr-systems induced by microwave irradiation [465]. The push-pull dipoles were generated from the rhodium(II)-cata-lyzed reaction of a diazo imide precursor containing a tethered heteroaromatic ring. In the example shown in Scheme 6.276, microwave heating of a solution of the diazo imide precursor in dry benzene in the presence of a catalytic amount of rhodium I) pivalate and 4 A molecular sieves for 2 h at 70 °C produced a transient cyclic carbonyl ylide dipole, which spontaneously underwent cydoaddition across the tethered benzofuran Jt-system to form a pentacyclic structure related to alkaloids of the vindoline type. 

The diester 226 undergoes ring-closure to the methylenecyclopentane derivative 227 in the presence of a catalytic amount of chlorotris(triphenylphosphine)rhodium in boiling chloroform saturated with hydrogen chloride. In contrast, if the reaction is catalysed by palladium(II) acetate, the isomeric cyclopentene 228 is produced (equation 115)118. 

The application of organostannanes in rhodium-catalyzed 1,4-addition reactions was first studied by Oi and co-workers.137,137a The treatment of enones or enolates with a slight excess of aryltrimethylstannane and catalytic amounts of [Rh(COD)(MeCN)2]BF4 generates the conjugate addition products in good yields. The use of protic additives enhanced the yield of the reaction (Scheme 48).138... 

The very first example of the catalytic reductive cyclization of an acetylenic aldehyde involves the use of a late transition metal catalyst. Exposure of alkynal 78a to a catalytic amount of Rh2Co2(CO)12 in the presence of Et3SiH induces highly stereoselective hydrosilylation-cyclization to provide the allylic alcohol 78b.1 8 This rhodium-based catalytic system is applicable to the cyclization of terminal alkynes to form five-membered rings, thus complementing the scope of the titanocene-catalyzed reaction (Scheme 54). 

Matsuda et al. recently described a domino reaction of 1,6-enyne derivatives with a hydrosilane and carbon monoxide in the presence of a catalytic amount of a rhodium complex to give a five-membered ring product containing a silylmethy-lene group.1761... 

The transition metal-catalyzed cyclopropanation of alkenes is one of the most efficient methods for the preparation of cyclopropanes. In 1959 Dull and Abend reported [617] their finding that treatment of ketene diethylacetal with diazomethane in the presence of catalytic amounts of copper(I) bromide leads to the formation of cyclopropanone diethylacetal. The same year Wittig described the cyclopropanation of cyclohexene with diazomethane and zinc(II) iodide [494]. Since then many variations and improvements of this reaction have been reported. Today a large number of transition metal complexes are known which react with diazoalkanes or other carbene precursors to yield intermediates capable of cyclopropanating olefins (Figure 3.32). However, from the commonly used catalysts of this type (rhodium(II) or palladium(II) carboxylates, copper salts) no carbene complexes have yet been identified spectroscopically. 

At this stage, we focused on the synthesis of a-silylketones 7 utilizing a rhodium-catalyzed isomerization of 6 to provide a new route to 4 and 5 (Scheme 6.3). As a result, neither 7 nor 8 was obtained from 6 in the presence of a catalytic amount of RhH(PPh3)4. However, when 9a (R=Ph) was present in 6a (R=Ph) as an impurity, 6a was isomerized in the presence of the rhodium catalyst, to afford the ketone 7a (R=Ph), thus providing the breakthrough for the studies outlined herein [4]. 

Initial attempts to extend this methodology to the catalytic manifold using Wilkinson s catalyst furnished only a trace amount of the cyclopentenone [38]. This is possibly due to an irreversible reaction between the nascent catalytic species and CO to exclude 63b from the coordination sphere (Scheme 11.17) [38d]. However, use of a catalytic amount of the cationic rhodium species [Rh(COD)(MeCN)2]Bp4 efficiently led to the formation of the [4+1] cycloadducts. 

Rhodium-catalyzed diazo insertions, known since 1976, have been extensively reviewed39. The first report40 indicated that rhodium acetate efficiently catalyzes diazo insertion into an alkene, giving the cyclopropane. Rhodium-catalyzed intramolecular C-H insertion was first observed by workers at Beecham Pharmaceuticals, who reported that 1, on exposure to a catalytic amount of rhodium acetate, cyclizes cleanly to the /1-lactam41. This approach to thienamycin derivatives has been developed further by these workers42,43. 

Metal ions in catalytic amounts exercise a profound influence on the course of the oxidation. In the absence of metal ions, the peracetic acid oxidation of 3-nitroaniline produces 3,3 -dinitroazoxybenzene. In the presence of traces of cupric ions and, to a lesser extent, in the presence of small quantities of iron, nickel, and rhodium salts, only 3,3 -dinitroazobenzene is formed. The oxidation of toluidines and aminophenols usually leads to tarry products [32]. 

Azoles containing an acidic NH-group, e.g. 3,5-dimethylpyrazole, react with various alcohols in the presence of a catalytic amount of ruthenium-, rhodium-, and iridium-trialkylphosphite complexes to afford the corresponding A-alkyl derivatives with excellent yields (92CL575). Regioselective A-alkylation was achieved using alkenes and sulfuric acid (89JHC3). 

Reaction of pyrido[2,l-6][l,3]thiazine-2,4-dione (105) with p-tosyl azide in the presence of triethylamine in acetonitrile at 0°C gave a 3-diazo derivative (106), which reacted with cyclohexene in the presence of a catalytic amount of rhodium acetate under reflux to yield a spiro derivative (107) [94H(39)219 95H(41)1631]. 

When ethylene was passed into a basic solution of Hg(OAc)2 containing a catalytic amount of [Rh2(OH)3(C5Me5)2]+, ethanol was formed.617 It appears that mercury salts of the type HOCH2CH2HgOAc are formed in a stoichiometric reaction so that this is not strictly a catalytic activation of ethylene by the rhodium complex. 

The rhodium diacetate dimer is used in catalytic amounts 0.132% (weight of dimer/weight of diazo ketone) has worked out to be the best ratio for this reaction. 

A methodology was reported in 2002 for the synthesis of (3-lactam fused enediynes [224]. When a solution of a diazo enediyne [225] was treated with a catalytic amount of rhodium acetate for 30 min, the (3-lactam fused enediyne was obtained as the only product, (Scheme 101). The yield in the carbene insertion step was about 50%, the rest being decomposition products. 

There has been great interest in recent years in methods for the generation of azomethine ylides and in exploitation of these reactive species in tandem/cascade processes for the rapid assembly of polyaza, polycyclic, multifunctional systems. a-Diazo ketones have featured greatly in such studies, treatment with a catalytic amount of rhodium(II) acetate generating transient rhodium carbenoids. A very common feature of many investigations of this type is the occurrence of quite unexpected reactions. For example, treatment of the diazo ketone 1 with a catalytic amount of... 

Allylic oxidation.2 t-Butyl hydroperoxide (0.5 equiv.) in acetic acid in the presence of catalytic amounts of this Rh30 complex (1) oxidizes cycloalkenes to a,/ -enones and the corresponding allylic acetates in the ratio of 6-7 1. Other rhodium complexes are less effective. Allylic alcohols (but not the acetates) are oxidized by this reaction to a,/ -enones. 

A similar reaction of ylide 200 can also be carried out under thermal conditions or in the presence of catalytic amounts of Cu(acac)2 [143]. The carbenoid reactions of iodonium ylides can also be effectively catalyzed by rhodium(II) complexes [144, 145]. The product composition in the rhodium(II) catalyzed reactions of iodonium ylides was found to be identical to that of the corresponding diazo compounds, which indicates that the mechanism of both processes is similar and involves metallocarbenes as key intermediates as it has been unequivocally established for the diazo decomposition [144]. 

The first step was development of a catalytic epoxidation cycle using stoichiometric amounts of achiral sulfides and rhodium acetate [212-214]. The nucleophilicity of the sulfide plays a key role. In addition, the absence of sulfides led to the formation of stilbenes, and homologated products were formed in the absence of rhodium acetate [214]. This emphasizes that the sulfide and the rhodium catalyst were required for the operation of the catalytic cycle shown in Scheme 6.87B [214], It was also found that the reaction proceeded to completion with catalytic amounts of the sulfide. A prerequisite is slow addition of the diazo compound over a longer period of time, e.g. 24 h, to avoid the assumed dimerization of the diazo compound as a competing reaction under those conditions [214, 215]. 

Enynes (77) can react with arylboronic acids in the presence of a catalytic amount of a rhodium(I) complex under mild conditions to give (Z)-l-(l-arylethyl- (g) idene)-2-vinylcyclopentanes (78).100 In analogy, the rhodium-catalysed cyclization of the cyano-substituted alkynes (79) with arylboronic acids has been reported to produce the cyclic ketone (80) as the first example of a nucleophilic addition of an Rh(I) species to a cyano group.101... 

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