Cyclopropanations copper acetate

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... 

CYCLOPROPANATION Copper-lsonitrile complexes. Cupric chloride. Diethylzinc-Bromoform-Oxygen. Palladium acetate. Titanium(IV) chloride-Lithium aluminum hydride. 

The majority of preparative methods which have been used for obtaining cyclopropane derivatives involve carbene addition to an olefmic bond, if acetylenes are used in the reaction, cyclopropenes are obtained. Heteroatom-substituted or vinyl cydopropanes come from alkenyl bromides or enol acetates (A. de Meijere, 1979 E. J. Corey, 1975 B E. Wenkert, 1970 A). The carbenes needed for cyclopropane syntheses can be obtained in situ by a-elimination of hydrogen halides with strong bases (R. Kdstcr, 1971 E.J. Corey, 1975 B), by copper catalyzed decomposition of diazo compounds (E. Wenkert, 1970 A S.D. Burke, 1979 N.J. Turro, 1966), or by reductive elimination of iodine from gem-diiodides (J. Nishimura, 1969 D. Wen-disch, 1971 J.M. Denis, 1972 H.E. Simmons, 1973 C. Girard, 1974),... 

The search for catalysts which are able to reverse the ratio of cyclopropane diastereomers in favor of the thermodynamically less stable isomer has met with only moderate success to date. Rh(II) pivalate and some ring-substituted Rh(II) benzoates induce cw-selectivity in the production of permethric acid esters 77,98 99 contrary to rhodium(II) acetate, which gives a 1 1 mixture 74,77,98), and some copper catalysts 98) (Scheme 10). 

Whereas metal-catalyzed decomposition of simple diazoketones in the presence of ketene acetals yields dihydrofurans 121,124,134), cyclopropanes usually result from reaction with enol ethers, enol acetates and silyl enol ethers, just as with unactivated alkenes 13). l-Acyl-2-alkoxycyclopropanes were thus obtained by copper-catalyzed reactions between diazoacetone and enol ethers 79 105,135), enol acetates 79,135 and... 

Intramolecular oxonium ylide formation is assumed to initialize the copper-catalyzed transformation of a, (3-epoxy diazomethyl ketones 341 to olefins 342 in the presence of an alcohol 333 . The reaction may be described as an intramolecular oxygen transfer from the epoxide ring to the carbenoid carbon atom, yielding a p,y-unsaturated a-ketoaldehyde which is then acetalized. A detailed reaction mechanism has been proposed. In some cases, the oxonium-ylide pathway gives rise to additional products when the reaction is catalyzed by copper powder. If, on the other hand, diazoketones of type 341 are heated in the presence of olefins (e.g. styrene, cyclohexene, cyclopen-tene, but not isopropenyl acetate or 2,3-dimethyl-2-butene) and palladium(II) acetate, intermolecular cyclopropanation rather than oxonium ylide derived chemistry takes place 334 ). 

In a direct comparison, it was found that with substrate 6, rhodium(II) acetate directs the reaction toward C-H insertion, to give cyclopentane 7, whereas copper-bronze favors alkene insertion, yielding the cyclopropane 845-46. A similar selectivity for cyclopropanation has been achieved by using amide ligands on the rhodium catalyst4. ... 

For cyclopropanation of very electron-rich alkenes such as vinyl ethers copper(II) trifluoroacetate, copper(II) hexafluoroacetylacetonate or rhodium(II) acetate are the catalysts of choice. Copper trifluoroacetate catalysed cyclopropanation of vinyldia-zomethane with dihydropyran gives the corresponding vinyl cyclopropane adduct in low yield (equation 17). In contrast, catalytic decomposition of phenyldiazomethane in the presence of various vinyl ethers results in high-yield phenylcyclopropane formation (equations 18 and 19)27. 

Intermolecular cyclopropanation of diazoketones is an effective method in organic synthesis. Wenkert and coworkers have applied this methodology to the synthesis of a substantial number of cyclopropane adducts 2868, 2969 and 307° which are synthetic intermediates in the preparation of natural products (equations 41—43). Copper catalysts were chosen for these transformations. Another interesting application of intermolecular cyclopropanation is to be found in Daniewski s total synthesis of an aromatic steroid. Palladium(II) acetate catalysed decomposition of 4-bromo-l-diazo-2-butanone in the presence of m-methoxystyrene was used to give the cyclopropyl ketone 31 which was a key intermediate in the total synthesis (equation 44)71. 

Carbenoid transformations involving competition between intramolecular cyclopropa-nation and /8-hydride elimination have been investigated149. The chemoselectivity of these catalytic transformations can be effectively controlled by the choice of catalyst. Rhodium(II) trifluoroacetate catalysed decomposition of diazoketone 111 proceeds cleanly to give only enone 112. However, rhodium(II) acetate or bis-(iV-t-butylsalicyladiminato) copper(II) cu(TBs)2 provides exclusively cyclopropanation product 113 (equation 102)149. 

The rhodium(II) catalysts and the chelated copper catalysts are considered to coordinate only to the carbenoid, while copper triflate and tetrafluoioborate coordinate to both the carbenoid and alkene and thus enhance cyclopropanation reactions through a template effect.14 Palladium-based catalysts, such as palladium(II) acetate and bis(benzonitrile)palladium(II) chloride,l6e are also believed to be able to coordinate with the alkene. Some chiral complexes based on cobalt have also been developed,21 but these have not been extensively used. 

Rhodium(II) acetate appears to be the most generally effective catalyst, and most of this discussion will center around the use of this catalyst with occasional reference to other catalysts when significant synthetic advantages can be gained. Cyclopropanation of a wide range of alkenes is possible with alkyl diazoacetate, as is indicated with the examples shown in Table l.l6e>37 The main limitations are that the alkene must be electron rich and not too sterically crowded. Poor results were obtained with trans-alkenes. Comparison studies have been carried out with copper and palladium catalysts and commonly the yields were lower than with rhodium catalysts. Cyclopropanation of styrenes and strained alkenes, however, proceeded extremely well with palladium(ll) acetate, while copper catalysts are still often used for cyclopropanation of vinyl ethers.38-40... 

The cyclopropanation of alkenes, alkynes, and aromatic compounds by carbenoids generated in the metal-catalyzed decomposition of diazo ketones has found widespread use as a method for carbon-carbon bond construction for many years, and intramolecular applications of these reactions have provided a useful cyclization strategy. Historically, copper metal, cuprous chloride, cupric sulfate, and other copper salts were used most commonly as catalysts for such reactions however, the superior catalytic activity of rhodium(ll) acetate dimer has recently become well-established.3 This commercially available rhodium salt exhibits high catalytic activity for the decomposition of diazo ketones even at very low catalyst substrate ratios (< 1%) and is less capricious than the old copper catalysts. We recommend the use of rhodium(ll) acetate dimer in preference to copper catalysts in all diazo ketone decomposition reactions. The present synthesis describes a typical cyclization procedure. 

Bicyclobutanes are also obtained from the catalytic decomposition of diazo compound 17492 (equation 51). Copper(I) iodide was the catalyst of choice, whereas rhodium(II) acetate did not show any activity in this case. When the related diazo compound 175 was decomposed, the product pattern depended in an unusually selective manner on the catalyst92. Intramolecular cyclopropanation leading to 176 is obviously less favorable than for carbene 172 and must yield to the 1,2-hydride shift not observed with the former carbene. The configuration of the resulting butadiene 177 can be completely reversed by the choice of the catalyst. 

Intramolecular cycloaddition of a diazo ketone to a cyclopropene. Rhodium) II) acetate is markedly superior to copper or copper(II) sulfate as the catalyst for cyclopropanation of l,4-diacetoxy-2-butyne with /-butyl diazoacetatc. The product (1) was converted by known steps into the diazo ketone 2. In the presence of rhodium(II) acetate, 2 undergoes intramolecular cycloaddition to the cyclopropene double bond to give the highly strained tricyclic pentanone derivative 3 in 30% yield. C oppcr catalysts are less efficient for this conversion. 

Unsaturated ethers. The efficient insertion of carboalkoxycarbenes into the O—H bond of alcohols catalyzed by Rh(II) acetate (5, 571-572) extends to reactions with unsaturated alcohols. For this reaction copper(II) triflate is usually comparable to rhodium(II) alkanoates. Insertion predominates over cyclopropanation in the case of ethylenic alcohols. In reactions with acetylenic alcohols, cyclopropenation can predominate over insertion because of steric effects, as in reactions of HC=CC(CH3)2OH where the insertion/addition ratio is 36 56. 

Studies involving cyclopropanation of glycals with ethyl diazoacetate in the presence of catalytic rhodium acetate or copper powder have also been reported <1995TL8901, 1996TL2533, 20010L2563>. 

In contrast to the carbene and carbenoid chemistry of simple diazoacetic esters, that of a-silyl-a-diazoacetic esters has not yet been developed systematically [1]. Irradiation of ethyl diazo(trimethylsilyl)acetate in an alcohol affords products derived from 0-H insertion of the carbene intermediate, Wolff rearrangement, and carbene- silene rearrangement [2]. In contrast, photolysis of ethyl diazo(pentamethyldisilanyl)acetate in an inert solvent yields exclusively a ketene derived from a carbene->silene->ketene rearrangement [3], Photochemically generated ethoxycarbonyltrimethyl-silylcarbene cyclopropanates alkenes and undergoes insertion into aliphatic C-H bonds [4]. Copper-catalyzed and photochemically induced cyclopropenation of an alkyne with methyl diazo(trimethylsilyl)acetate has also been reported [5]. 

Improved reaction. Conia et al. have reported two modifications of the Simmons-Smith reaction which ave improved yields. One is the use of a zinc-silver couple in place of the zinc copper couple. This couple is prepared by adding granular zinc to a stirred hot solution of silver acetate in acetic acid. The mixture is stirred for 30 sec. and the zinc-silver couple formed is isolated by decantation and washed with acetic acid and ether. It is then stabilized by addition of a small amount of silver wool. The second improvement is that the reaction mixture is not subjected to acid hydrolysis. Instead an amine, for example pyridine, is added. This forms the insoluble complexes Znlj-C HsN and ICH jZnl -(C, 115N)j the cyclopropane products are then isolated from the filtrate. 

Carbenic fragmentation is formally the reverse of addition of carbenes to the sulfur atom of the thiophene ring, and has been observed only with 2,5-dichlorothiophenium bis(alkoxycarbonyl)methylides (30). When 30 (R = CHj) is heated at 110°C in refluxing toluene in the presence of rhodium(II) acetate or copper(II) acetylacetonate, fragmentation of the ylid to 2,5-dichlorothiophene and the carbenoid occurs. The bis(methoxycarbonyl)-carbene has been trapped with alkenes to produce high yields of the cyclopropanated products (78CC641). Since the ylid is a stable crystalline solid with a long shelf life, it represents a convenient source of bis-(methoxycarbonyl)carbene. 

Methylene ( CH2) generated photochemically or thermally from diazomethane is highly reactive and is prone to incur side reactions to a substantial extent. In order to avoid these undesirable complexities, the cyclopropanation of multiple bonds with diazomethane has usually been carried out under catalytic conditions The catalysts most frequently employed are copper salts and copper complexes as well as palladium acetate. The intermediate produced in the copper salt-catalyzed reactions behaves as a weak electrophile and exhibits a preference to attack an electron-rich double bond. It is also reactive enough to attack aromatic nuclei. In contrast, the palladium acetate-catalyzed decomposition of diazomethane cyclopropanates a,a- or a,jS-disubstituted a,jS-unsaturated carbonyl compounds in high yields (equation 47). The trisubstituted derivatives, however, do not react. The palladium acetate-catalyzed reaction has been applied also for the cyclopropanations of some strained cyclic alkenesstyrene derivatives and terminal double bondsHowever, the cyclopropanation of non-activated, internal double bonds occurs only with difficulty. The difference, thereby. 

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