Rhodium acetate, reaction with diazo

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-... 

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]. 

One of the key steps in building the fused ring involves the reaction of the activated acetoacetate methylene group in that compound with toluenesulfonyl azide to give the diazo intemediate (12-1). Treatment of that product with rhodium acetate leads to a loss of nitrogen with the consequent formation of carbene (12-2) this inserts into the adjacent amide N—H bond to form a five-membered ring and thus the carbapenem (12-3) [15]. The first step in the incorporation of the thioenol function consists in the conversion of the ketone to the enol phosphate derivative... 

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]. 

The products formed in these reactions are very sensitive to the functionality on the carbenoid. A study of Schechter and coworkers132 using 2-diazo-1,3-indandione (152) nicely illustrates this point. The resulting carbenoid would be expected to be more electrophilic than the one generated from alkyl diazoacetate and consequently ihodium(II) acetate could be used as catalyst. The alkylation products (153) were formed in high yields without any evidence of cycloheptatrienes (Scheme 33). As can be seen in the case for anisole, the reaction was much more selective than the rhodium(II)-catalyzed decomposition of ethyl diazoacetate (Scheme 31), resulting in the exclusive formation of the para product. Application of this alkylation process to the synthesis of a novel p-quinodimethane has been reported.133 Similar alkylation products were formed when dimethyl diazomalonate was decomposed in the presence of aromatic systems, but as these earlier studies134 were carried out either photochemically or by copper catalysis, side reactions also occurred, as can be seen in the reaction with toluene (equation 36). 

Cyclization to a morpholinolactone (59) occurs in the hydrolysis reaction of the di-A-hydroxylethylated compound (60). Compound (59) is rapidly hydrolysed by water to (61) but in file presence of equimolar amounts of amines (RNH2) or ammo acid derivatives (62) forms.56 A novel reaction of cyclic 2-diazo-l,3-dicarbonyl compounds (63) with lactones (64) affords the products (65) in the presence of rhodium acetate, Rh2(OAc)4.57 Lewis acid-promoted intramolecular additions of allylsilanes to lilac tones gave substituted cyclopentanes.58 A proposed transition state guided efforts to improve the stereoselectivity of the reaction. The reaction of a series of /1-lactone derivatives, such as (66)-(68), has been studied and they have been ling cleaved the reaction outcome is both Lewis acid and structure dependent.59... 

Oxathiepins have been obtained from the reaction of 2//-l-benzothiete with diazo compounds in the presence of rhodium acetate (Equation 18) <1995TL6047>. 

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]. 

Alkenylselenonium salts 390 undergo cyclization on treatment with sodium hydride to provide a useful approach to benzoxathiepins 391 (Scheme 208) <2000JOC8893, CHEC-III(13.12.8.2)374>. Benzoxathiepins have also been prepared by the reaction of 2//-l-benzothiete with diazo compounds in the presence of rhodium acetate (Scheme 209) <1995TL6047, CHEC-III(13.12.9)377>. 

The reactions illustrated in equations (62-64) are each catalyzed by rhodium acetate. Diazo compounds, especially diazoalkanes, can also react by a simple ionic mechanism. The esterification of a carboxylic acid with diazomethane is a familiar example. The ionic pathway is especially likely when the intermediate carbocation would be stabilized. Thus, diazine (158) couples smoothly with phenols, presumably by thermal rearrangement to the corresponding diazo sugar, followed by acid-catalyzed N2 loss... 

The oxepino[2,3-d]isoxazol system 408 was prepared in 77% yield from diazo ester 409 and DMAD with a rhodium(II) acetate catalyst. The transient furoisoxazole 410 undergoes 1,5-electrocyclization to a carbene, which yields the final products via reaction with DMAD followed by a series of consecutive transformations (91TL1161). 

The rhodiumcarbene intermediate, which is believed to be the active species in rhodium acetate catalyzed cyclopropanations with diazo compounds, shows electrophilic reactivity. Thus, diazopropenes preferentially add to electron-rich alkenes, demonstrated by the reaction of 3-diazo-l,l-dichloropropene (15) with 2-trimethylsiloxybuta-l,3-diene (16) . A mixture of Z-configurated divinylcyclopropanes 17 and rearranged dienones 18 was obtained (see also Section 1. B.2.4.5.1. for further examples of the formation of seven-membered rings such as 18). 

Allyldiethylamine behaves similarly, but the yields are low since neither the starting amine nor the products are stable to the reaction conditions. For the efficiency of the cyclopropanation of the allylic systems under discussion, a comparison can be made between the triplet-sensitized photochemical reaction and the process carried out in the presence of copper or rhodium catalysts whereas with allyl halides and allyl ethers, the transition metal catalyzed reaction often produces higher yields (especially if tetraacetatodirhodium is used), the photochemical variant is the method of choice for allyl sulfides. The catalysts react with allyl sulfides (and with allyl selenides and allylamines, for that matter) exclusively via the ylide pathway (see Section 1.2.1.2.4.2.6.3.3. and Houben-Weyl, Vol. E19b, pll30). It should also be noted that the purely thermal decomposition of dimethyl diazomalonate in allyl sulfides produces no cyclopropane, but only the ylide-derived product in high yield.Very few cyclopropanes have been synthesized by photolysis of other diazocarbonyl compounds than a-diazo esters and a-diazo ketones, although this should not be impossible in several cases (e.g. a-diazo aldehydes, a-diazocarboxamides). Irradiation of a-diazo-a-(4-nitrophenyl)acetic acid in a mixture of 2-methylbut-2-ene and methanol gave mainly l-(4-nitrophenyl)-2,2,3-trimethylcyclo-propane-1-carboxylic acid (19, 71%) in addition to some O-H insertion product (10%). ... 

Photochemical decomposition of diazo(trimethylsilyl)methane (1) in the presence of alkenes has not been thoroughly investigated (see Houben-Weyl Vol. E19b, p 1415). The available experimental data [trimethylsilylcyclopropane (17% yield) and la,2a,3j8-2,3-dimethyl-l-trimethylsilylcyclopropane (23% yield)] indicate that cyclopropanation occurs only in low yield with ethene and ( )-but-2-ene. In both cases the formal carbene dimer is the main product. In reactions with other alkenes, such as 2,3-dimethylbut-2-ene, tetrafluoroethene or hexafluoro-propene, no cyclopropanes could be detected.The transition-metal-catalyzed decomposition of diazo(trimethylsilyl)methane (1) has been applied to the synthesis of many different silicon-substituted cyclopropanes (see Table 3 and Houben-Weyl Vol.E19b, p 1415) 3.20a,b,2i.25 ( iQp. per(I) chloride has been most commonly used for carbene transfer to ethyl-substituted alkenes, cycloalkenes, styrene, and related arylalkenes. For the cyclopropanation of acyl-substituted alkenes, palladium(II) chloride is the catalyst of choice, while palladium(II) acetate was less efficient, and copper(I) chloride, copper(II) sulfate and rhodium(II) acetate dimer were totally unproductive. The cyclopropanation of ( )-but-2-ene represents a unique... 

Thioamides of two cyclopropanecarboxylic acids undergo coupling reactions with diazomethane derivatives in refluxing benzene containing rhodium(II) acetate. The reaction conceivably takes place via a thiirane intermediate which undergoes reductive elimination by reaction with excess diazo compound. An example of an intramolecular reaction is the formation of indolizine 2. If the diazo compound is not in excess a thiol is formed, this can be removed by Raney nickel desulfurization. ... 

The reaction of an a-nitro diazo compound with an alkyne in the presence of rhodium acetate gave a range of 3-nitrocyclopropenes. ... 

RHODIUM(II) ACETATE-CATALYZED REACTION OF ACETYLENES WITH DIAZO CARBONYL COMPOUNDS ... 

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]). 

Diazo-5,5-dimethylcyclohexan-l,3-dione (140) with an excess of acrylate esters serving as both reactant and solvent in the presence of rhodium acetate afforded benzofuran 141 (98SC865). The formation of the dihydrofurans probably proceeded via a 1,3-dipolar cycloaddition of a metal carbenoid to the x,/)-unsa titrated ester (98SC865). Similarly, the reaction can take place with dihydrofuran, furan, and 1-acetyl indole to give 109,142, and 143, respectively (91JOC6269) (Scheme 24). 

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