Rhodium catalysed reactions

Helquist s work on the use of diazomalonate in the synthesis of oxazoles has been extended to other diazocarbonyl compounds in our own laboratory.<92TL7769, 94T3761> Thus it was found that sulfonyl-, phosphonyl- and cyano-substituted diazoesters gave the corresponding 4-functionalised oxazoles 30 in acceptable yield (Scheme 20). In many cases the yield of oxazole was significantly improved by the use of rhodium(II) trifluoroacetamide as catalyst. The 4-cyano-oxazole 30 (R = Me, Z = CN) proved interesting in that it allowed the formation of a bis-oxazole 31 by a second rhodium catalysed reaction (Scheme 20). 

Iodonium ylides (136), generated in situ with bisacetoxyiodobenzene, are converted to allyl- or benzyl-substituted oxonium or sulfonium ylides (137) via rhodium- or copper-catalysed carbene transfer.115 Such ylides undergo [1,2]- or [2,3]-rearrangement to the corresponding 2-substituted heterocycles (138). An example of the rhodium-catalysed reaction is reported in Scheme 36. 

Larger rings such as (36) were made by insertion of a rhodium carbenoid into phenolic OH bonds.37 Triarylamines have been isolated from a rhodium-catalysed reaction of diarylamines with 2-diazocyclohexane-l,3-dione 38... 

The rhodium-catalysed reaction between simple alkenes (50) and bis(catecholato) diboron (51) has been reported to result in the syn addition of the diboron across the alkene. The l,2-bis(boronate) thus obtained was subsequently oxidized to provide the corresponding 1,2-diol (52). In the presence of QUINAP ligand, high enantioselection in the diboration was attained. The reaction was found to be highly selective for trans- and trisubstituted alkenes and can also be selective for some monosubstituted alkenes.59... 

Reaction of the stabilised iodonium ylide 8 with ketones gives the dioxoles 9 <02TL5997> and rhodium catalysed reaction of Me02C-C(=N2)-CF3 with aldehydes similarly gives 10 <02OL2453>. A general synthesis of l,3-dioxol-2-ones has been described... 

Other new oxathiolane syntheses include reaction of an epoxide with a stable thioketone <01HCA3319>. Rhodium catalysed reaction of dimethyl diazomalonate with a thioketone has been used to prepare oxathiole 92 <02PJC551> and the iodonium ylide 8 reacts with thioketones or carbon disulfide to form oxathioles <02TL5997>. 

As a step in the synthesis of a higher homologue of the antibiotic thienamycin, the closure of the pyridine ring is effected by warming the diazo ester (793) with rhodium(II) acetate (review of rhodium-catalysed reactions [3928]) the product (79.6, R = H) is more easily isolated and purified as its O-tosyl derivative (79.6, R = Ts). Intramolecular homolytk cyclization (the Pschorr reaction) of the diazonium salt of N-methylbenzanilide gives moderate yields which are comparable with those given by the pyrolytic cyclization of the 2-iodo analogue (see Chapter 90, Section II.2 [2303]). 

Aryl silicon compounds can be prepared by metal-catalysed reaction of halides with silanes, as in the rhodium-catalysed reaction below. The mechanistic details of this reaction (probably) differ from the palladium-catalysed borane reaction. (NOTE triethoxy silane is extremely toxic )... 

The rhodium-catalysed reaction between 1,3-azoles and terminal alkenes is thought to proceed via a carbene complex. ... 

Carbenoid ring-expansion of thiophen to a 2/f-thiopyran has been observed in the rhodium-catalysed reaction with (132), which gave (133) and (134). Evidence has been presented that the nitrene intermediate (135), obtained from the corresponding nitro- or azido-derivatives in the usual way, first gives the aziridine intermediate (136), which then leads to interesting heteropolycyclic systems such as 3-(2-thienyl)indole derivatives. ... 

An attempt to prepare <2) eq. <73) -from PhNH2 and butanal was unsucces-ful. The rhodium catalysed reactions (even wi th J]RhCl (NBD>32 is catalyst) give (1) in excellent yields. Thus -formation pathway should be di-f-ferent between (1) and (2) 5 via aniline -for (1), as -for the cases previously discussed, and a nitrene or other -for (2), contrary to what has been proposed in the case o-f the reactions catalysed by the [fth(CO)2CI32"MoC15 system] 18. ... 

The palladium catalysed reaction -follows a rate law which is independent on the substrate concentration, but dependent on the CO pressure. In a later work, a AS =-233 J mol " "K, instead o-f -414, has been reported -for this react i on [1843, tor which it has been confirmed a zero order in substrate and first order in each metallic component and in CO pressure. The carbonyl ation of an intermediate complex forming the isocyanate is considered the rate determinin step in the palladium-catalysed reaction. In this work[183j, the oxidative addition of the nitro compound to the catalyst was considered a more likely rate determining step in the case of the rhodium-catalysed reaction. 

There has been a review of asymmetric Friedel—Crafts reactions. It has been shown that the rhodium-catalysed reaction of potassium phenyltrifluoroborate with A-tosyl ketimines may lead to products such as (18) with high enantioselectivity. (g) The reaction of A-t-butanesuUinylimino esters with arenes to give products (19) is catalysed by Lewis acids, such as indium triflate, and may lead to enantio-metrically enriched a-glycines. The intramolecular alkylation of hydrogenated 0 tetralins, shown in Scheme 2, using iron(III) or aluminium(III) catalysts yields cis-hexahydrobenzophenanthridines. Formation of a stabilized carbocation intermediate is... 

The rhodium-catalysed reaction of 2-germylphenylboronic esters (79) with alkynes has been designed as a modular method for the synthesis of benzogermoles (80). The reaction proceeds through the unusual activation of the C sp ) G bond. ... 

Syntheses of 3-deoxy-2-ulosonic acids have again been the subject of a number of reports. The cycloheptene derivative 46 was made by enzymic desymmetrization of the neso-compound and employed in a multistep synthesis of the doivadve 47 of 3-deoxy-D-ara6ino-heptulosonic acid (Dah), dihydroxylation being used to establish the required chirality at C-S and C-6 of the sugar relative to that at C-4.39 if, in the chemistry of Scheme 6, the final rhodium-catalysed reaction was replaced by MCPBA oxidation, Kdo could be obtained. Application of the earlier stages of... 

The additions of monohydrosilanes to terminal alkynes catalysed by chloro-platinic acid involves stereoselective (100%) cw-addition. However, in the presence of [RhCl(PPh3)3l as catalyst stereoselective /ra j-addition is observed, results which resemble peroxide-catalysed reaction of trichlorosilanes with alkynes. The rhodium-catalysed reactions may involve radical species. ... 

Ishida, N. Sawano, S. Murakami, M. Synthesis of 3,3-Disubstituted [Small Alphaj-Tetralones by Rhodium-Catalysed Reaction of l-(2-haloaryl) Cyclobutanols. Chem. Commun. 2012,48,1973-1975. 

A new synthesis of indoles employs a rhodium-catalysed reaction between hydrazines and aldehydes or ketones. This process, therefore, is equivalent to the Fischer synthesis under non-acidic conditions. However, the yields in these reactions are not particularly high, and reaction temperatures of ca. 200 C are... 

Baldwin s rules can account for the unprecedented ring expansion, whereby poly-oxygenated eight- and nine-membered rings are formed regioselectively by rhodium-catalysed reaction of cyclic acetals with a-diazo -ketoesters and diketones under mild conditions. ... 

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