Rhodium, acetate

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%). 

The use of dirhodium(II) catalysts for catalytic reactions with diazo compounds was initiated by Ph. Teyssie [14] in the 1970s and rapidly spread to other laboratories [1]. The first uses were with dirhodium(II) tetraacetate and the more soluble tetraoctanoate, Rh2(oct)4 [15]. Rhodium acetate, revealed to have the paddle wheel structure and exist with a Rh-Rh single bond [16], was conve-... 

Aziridination of alkenes can be carried out using N-(p- to I ucncsu I I o n y I i m i n o) phenyliodinane and copper triflate or other copper salts.257 These reactions are mechanistically analogous to metal-catalyzed cyclopropanation. Rhodium acetate also acts as a catalyst.258 Other arenesulfonyliminoiodinanes can be used,259 as can chloroamine T260 and bromoamine T.261 The range of substituted alkenes that react includes acrylate esters.262... 

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). 

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>. 

For the synthesis of permethric acid esters 16 from l,l-dichloro-4-methyl-l,3-pentadiene and of chrysanthemic acid esters from 2,5-dimethyl-2,4-hexadienes, it seems that the yields are less sensitive to the choice of the catalyst 72 77). It is evident, however, that Rh2(OOCCF3)4 is again less efficient than other rhodium acetates. The influence of the alkyl group of the diazoacetate on the yields is only marginal for the chrysanthemic acid esters, but the yield of permethric acid esters 16 varies in a catalyst-dependent non-predictable way when methyl, ethyl, n-butyl or f-butyl diazoacetate are used77). 

The rhodium acetate catalyzed addition of ethyl diazoacetate to MCP (1) gave spiropentane 619 in high yield (Scheme 89) [6e]. The same compound 619 was obtained in lower yield by a Simmons-Smith reaction to methylenecyclo-propane 217 [164],... 

The "real" oxo precatalyst [HRh(CO)(TPPTS)3] is easily made in the oxo reactor by reacting suitable Rh salts (e.g., rhodium acetate or rhodium 2-ethylhexanoate) with TPPTS - both components freshly prepared or recovered and recycled - without any additional preformation step. The reaction starts after formation of the active species and adjustment of the whole system with water to the desired P/Rh ratio (ensuring the stability of the catalyst and the desired n/iso ratio). 

The rhodium acetate complex catalyzed the intramolecular C-H insertion of (/ )-diazo-fR)-(phenylsulfonyl)acet-amides 359 derived from (f )-amino acids to afford in high yield the 6-benzenesulfonyl-3,3-dimethyl-7-phenyl-tetrahydro-pyrrolo[l,2-c]oxazol-5-one 360 (Equation 63) <2002JOC6582, 2005TL143>. 

Unfortunately, for all these reasons the conclusions cannot be applied quantitatively for description of the pH effects in the RCH-RP process. There are gross differences between the parameters of the measurements in [97] and those of the industrial process (temperature, partial pressure of H2, absence or presence of CO), furthermore the industrial catalyst is preformed from rhodium acetate rather than chloride. Although there is no big difference in the steric bulk of TPPTS and TPPMS [98], at least not on the basis of their respective Tolman cone angles, noticable differences in the thermodynamic stability of their complexes may still arise from the slight alterations in steric and electronic parameters of these two ligands being unequally sulfonated. Nevertheless, the laws of thermodynamics should be obeyed and equilibria like (4.2) should contribute to the pH-effects in the industrial process, too. 

Decomposition of diazoketone 110 with rhodium acetate produced the highly electrophilic rhodium stabilized metallocarbenoid that suffers attack by the Lewis basic oxygen of the pendant ketone, producing cyclic carbonyl ylide 111. This ylide was trapped by the addition of an activated acetylene such as DMAD to furnish... 

Decomposition of diazoketone 113 with rhodium acetate led to the formation of a tethered cyclic carbonyl ylide 114 that was poised to undergo an intramolecular cycloaddition, preparing 115 in 60% yield. Interestingly, if DMAD was added to the reaction mixture, the only product arose from intermolecular cycloaddition. 

Padwa et al. (42,43) investigated the cyclization of diazoalkynyl ketones such as 116 and found that upon exposure to rhodium acetate, the transient metallocarbenoid... 

Padwa et al. (48) examined the behavior of diazoketone 127 under rhodium catalysis and found that the ligands associated with rhodium had a dramatic effect on the distribution of products 128 (from the carbonyl ylide) and 129 (from intramolecular C—H insertion). When rhodium acetate was employed there was a... 

Wenkert and Khatuya (51) examined the competition between direct insertion of a carbene into furan (via cyclopropanation) and ylide formation with reactive side-chain functionality such as esters, aldehydes, and acetals. They demonstrated the ease of formation of aldehyde derived carbonyl ylides (Scheme 4.30) as opposed to reaction with the electron-rich olefin of the furan. Treatment of 3-furfural (136) with ethyl diazoacetate (EDA) and rhodium acetate led to formation of ylide 137, followed by trapping with a second molecule of furfural to give the acetal 138 as an equal mixture of isomers at the acetal hydrogen position. 

Treatment of proline derivative 154 with rhodium acetate (57) originally led to ylide 155. However, this ylide (155) quickly rearranges to the more stable azomethine ylide 156, which undergoes cycloaddition with DMAD to give the unusual adduct 157. Intramolecular trapping experiments (58,59) have also been conducted (Scheme 4.35). 

Note that intramolecular cycloadditions were also plausible with the correct substitution and tether length. Bien and co-workers (71,72) found that addition of rhodium acetate to a-diazoketone 170 produced three products with the major outcome being the oxatricyclic 171 and a minor amount of the diastereomeric intramolecular cyclopropanes 172 (Scheme 4.39). 

Dauben s group utilized the same retrosynthetic disconnections, but chose to add more functionality to the cycloaddition precursor. From a simple frawi-disubstituted cyclopentane, Dauben used an aldol reaction of a cyclopropylvinyl aldehyde to prepare the cycloaddition precursor. The diazo-substituted (3-ketoester was completed using a Roskamp-Padwa coupling followed by diazo-transfer. Addition of rhodium acetate to the diazo substituted p-ketoester 179 led to an excellent 86% yield of the correct diastereomer (Scheme 4.42). 

Harwood and co-workers (105) utihzed a phenyloxazine-3-one as a chiral derived template for cycloaddition (Scheme 4.50). An oxazinone template can be formed from phenylglycinol as the template precursor. The diazoamide needed for cycloaddition was generated by addition of diazomalonyl chloride, trimethyl-dioxane-4-one, or succinimidyl diazoacetate, providing the ester, acetyl, or hydrogen R group of the diazoamide 198. After addition of rhodium acetate, A-methylmaleimide was used as the dipolarophile to provide a product that predominantly adds from the less hindered a-face of the template in an endo fashion. The cycloaddition also provided some of the adduct that approaches from the p-face as well. p-Face addition also occurred with complete exo-selectivity. Mono- and disubstituted acetylenic compounds were added as well, providing similar cycloadducts. 

Friedrichsen and co-workers (133) approached substituted benzotropolones from an aromatic substituted carbonyl ylide with a tethered alkyne as the intramolecular dipolarophUe (Scheme 4.67). Starting from an aromatic anhydride, Friedrichsen was able to make the tethered alkyne via addition of either pentyn-ol or hexyn-ol, then transform the recovered benzoic acid to the a-diazocarbonyl cycloaddition precursor. Addition of rhodium acetate resulted in the tandem formation of cyclic carbonyl ylide followed by cycloaddition of the tethered alkyne producing the tricyclic constrained ether 252. Addition of BF3 OEt2 opened the ether bridge, forming the benzotropylium ion, which subsequently rearranged to form the tricyclic benzotropolone (253). 

Hodgson et al. (138) chose to investigate a system that had previously been shown to undergo an effective intramolecular addition of a tethered olehn (Scheme 4.72). In his first attempt, using Doyle s Rh2[(5/ )-MEPY]4, the yield of cycloadduct 270 obtained was comparable to that with rhodium acetate, but no asymmetric induction was observed. Changing to the Davies catalysts in dichloromethane resulted in a... 

The reaction of a thiocarbonyl and a-oxodiazo compound that leads to 1,3-oxathioles has been rationalized by a 1,5-dipolar electrocyclization reaction (178). It was suggested that an intermediate thiocarbonyl yhde bearing a C=0 function at the a-position (extended dipole) was first formed. Due to the low reactivity of a-oxodiazo compounds, these reactions were carried out at elevated temperatures or in the presence of rhodium acetate as the catalyst. In some cases, catalysis by LiC104 was also reported (77-80). 

Maier and Schoffling (37) extended this intramolecular isomiinchnone cycloaddition to a synthesis of fused furans by employing an alkyne dipolarophile (Scheme 10.9). Thus, the diazo acetylenes (66) are smoothly converted to furans (69) via isomtinchnones (67) with catalytic rhodium acetate. 

The total synthesis of the antifungal alkaloid K252a has been reported in which the indolocarbazole nucleus is constructed using novel rhodium carbenoid chemistry <1995JA10413, 1997JA9641>. Thus, reaction of 2,2 -biindole with diazolactam 173 in the presence of rhodium acetate in degassed pinacolone produces indolocarbazoles in moderate yields (Equation 107). 

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. 

It was then demonstrated38 that cyclization of 3 proceeded much more efficiently with rhodium acetate than with copper salt catalysis (no cyclization with copper sulfate). 

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