Diazo esters decomposition

A good example for a detailed Hammett correlation study is the rhodium(II)-catalyzed decomposition of a-diazo esters. The most likely mechanism for the a-diazo ester decomposition process involves the initial complexation of the nega-... 

The starting diazo esters 110 were prepared by diazo transfer from the corresponding malonate esters 109. A selection of chiral Hgands in conjunction with 2mol% (with respect to the diazo compound) of [Cu(OTf)2] in (CH2C1)2 was then examined at 65 °C (Scheme 31). All of the Hgands tested were sufficiently reactive to produce diazo decomposition at 65 °C, although the yields of cyclopropanation products were quite variable. Even tertiary... 

The combined ether solutions are then subjected to distillation at 20° or below under the vacuum obtainable from a water pump until all the ether is removed. Prolonged distillation results in decomposition of the diazo ester and in a decreased yield. The yellow residual oil is practically pure ethyl diazoacetate and is satisfactory for most synthetic purposes (Note 3). The yield is about 98 g. (85%) (Notes 4 and 5). 

Decomposition of the diazo ester 395 in presence of dirhodium tetraacetate gives the zwitterionic intermediate 396, which undergoes a 1,3-dipolar cycloaddition with the double bond of the adjacent vinylindole. The bridged compound is isolated in good yield when the reaction is carried out at room temperature however, at 50 °C or above, compound 397 is the only compound isolated, again in good yield (Scheme 93) <2005JOC2206>. 

In 1966, Nozaki et al. reported that the decomposition of o-diazo-esters by a copper chiral Schiff base complex in the presence of olefins gave optically active cyclopropanes (Scheme 58).220 221 Following this seminal discovery, Aratani et al. commenced an extensive study of the chiral salicylaldimine ligand and developed highly enantioselective and industrially useful cyclopropanation.222-224 Since then, various complexes have been prepared and applied to asymmetric cyclo-propanation. In this section, however, only selected examples of cyclopropanations using diazo compounds are discussed. For a more detailed discussion of asymmetric cyclopropanation and related reactions, see reviews and books.17-21,225... 

Ethyl 2-fluoroethoxyacetate, F [CH2]2 0 CH2 C02Et, could not be prepared by the action of ethyl diazoacetate on pure redistilled 2-fluoroethyl alcohol, and the addition of a small quantity of concentrated hydrochloric acid had no effect, which is rather surprising in view of the known catalytic action of acids on the decomposition of the diazoacetic ester. However, fluoroethyl alcohol which had not been specially dried reacted immediately with ethyl diazoacetate with a vigorous evolution of nitrogen and the simultaneous disappearance of the yellow colour of the diazo ester. 

Whereas base-induced decomposition of N-nitrosourethanes has been utilized (9) as a popular method of generating diazoalkanes, only limited investigations on base treatments of nitrosamides have been reported (10). The primary product in the base treatment is assumed, in analogy to better investigate nitrosourethane cases, to be diazo hydroxides V via attack of a base on the carbonyl group as in IV. A diazo hydroxide V has been related to the diazo ester III by a reaction with benzoyl chloride. 

In addition to copper and rhodium catalysts commonly used in the generation of metal carbene complexes, other transition metals have also been explored in the diazo decomposition and subsequent ylide generation.Che and co-workers have recently studied ruthenium porphyrin-catalyzed diazo decomposition and demonstrated a three-component coupling reaction of a-diazo ester with a series of iV-benzylidene imines and alkenes to form functionalized pyrrolidines in excellent diastereoselectivities (Scheme 20). ... 

Functionalized cyclopropenes are viable synthetic intermediates whose applications [99.100] extend to a wide variety of carbocyclic and heterocyclic systems. However, advances in the synthesis of cyclopropenes, particularly through Rh(II) carboxylate—catalyzed decomposition of diazo esters in the presence of alkynes [100-102], has made available an array of stable 3-cyclopropenecarboxylate esters. Previously, copper catalysts provided low to moderate yields of cyclopropenes in reactions of diazo esters with disubstituted acetylenes [103], but the higher temperatures required for these carbenoid reactions often led to thermal or catalytic ring opening and products derived from vinylcarbene intermediates (104-107). 

The decomposition of a-diazo esters by a ruthenium porphyrin catalyst has been used by Che and co-workers in a multicomponent strategy directed toward functionalized pyrrolidines 172. The first step involves the formation of a ruthenium... 

Cyclopropyl lactones. Copper-catalyzed decomposition of unsaturated esters of dia-zoacetic acid can provide eyclopropyl lactones >2, 83). The soluble copper chelate 1 is superior for this purpose to copper powder or copper oxide. In a typical example, the lactone 3 is obtained from the diazo ester 2 in 92% yield. 

Carbene insertion into the O-H bond of alcohols is especially versatile for the formation of ethers. Diazomethane has been used, but other diazo compounds have also been used even those with fluorine in the carbene species. Rhodium acetate seems to be the catalyst of choice for the decomposition of a-diazo esters. Different alcohols 21 react with compound 22 to give fluorinated ethers 23 in good yield. ... 

Diazo Esters.—Before taking up the reactions of decomposition of diazo compounds there is one other class of derivatives which should be mentioned. As an acid compound benzene diazo hydroxide yields esterSy not by the direct action of alcohols, but by the action of alkyl halides upon silver diazotate. These esters are stable compounds like... 

Alkoxycarbonylmethylenes have also been transferred from dibromoacetic ester with copper as well as from haloacetic esters with Cu20/RNC In the reactions of terminal alkenes, the former reagents give syn-adducts preferentially. The triplet sensitized decomposition of 2-diazopropionic ester in alkenes gives 1-methylcyclopropanecarboxylic esters (equation In contrast, the direct photolysis of the same diazo ester produces... 

The intramolecular insertion into the N—H bond of j8-lactams was used successfully in the synthesis of bicyclic ring systems. Photochemical, in contrast to Rh(II)-catalyzed, decomposition of diazo ester 62 was found to occur far less selectively. In the photolytic reaction, the imide 63 is the major product. It presumably arises by a photolytic Wolff rearrangement to a ketene intermediate, which is trapped intramolecularly. With Rh2(AcO)4 catalyst the Wolff rearrangement is suppressed and 62 undergoes ring closure to 64 nearly quantitatively (80TL31). 

The copper-catalyzed pyrolysis of diazo ketone 139 (R = O, R = H) gives pyrrolizine 140 in quantitative yield (83HCA2666). However, the decomposition of diazo ester 139 (R = H2, R = C02Et) is not preparatively useful, since a mixture of 141 and ester 142 was obtained in a yield of 35%, at best (83CJC454). 

When a carbene center and a nitrogen are linked by a four-carbon chain, insertion into the N — H bond gives rise to piperidine derivatives. The rhodium(II) acetate-catalyzed decomposition of either diazo ketones 158 (92TL6651) or diazo ester 159 (85JOC5223) leads to insertion into the amide N — H bond to give products in moderate yields. Various solvents, temperatures, and catalyst concentrations were found to be important in determining the yield and the product distribution in the cyclization of 159. 

Photolytic and catalytic decomposition of a-diazo esters produces )8-lactones, which are formed via intramolecular C—H insertion of a carbene or carbenoids. Tertiary alkyl esters of diazomalonic acid are decomposed by rhodium acetate with exclusive formation of the four-membered ring 211. This suggests a smooth insertion into the C—H bond activated by the adjacent oxygen atom (90TL1023). jS-Lactone 212 was obtained by photolysis of diazo malonic ester 213 (71CC577). 

Intramolecular cyclopropanation of olefinic a-diazo ketones and a-diazo esters has been widely used in organic synthesis. When a carbenoid center and the double bond are separated by a chain of three atoms, one of which is oxygen, a five-membered O-containing heterocycle is formed. Intermolecular cyclopropanations of olefins are known to allow stereospecific formation of desired products. Thus, decomposition of substituted allyl diazomalonates 265 in the presence of copper salts gives rise to bicyclic... 

Rhodium(II) octanoate-catalyzed decomposition of diazo esters 52, involving in the first stage a reaction of a carbenoid with the pyrrole double bond, furnishes polycyclic lactones 53 (34-79% R = H, Me R = H, Ph) (94TL5209) as shown in Scheme 18. 

A similar change of mechanism is observed in the reaction of silyl-substituted diazo esters 559 with acetaldehyde and benzaldehyde. The Rh2(pfb)4-induced decomposition of allyl ester 559 (n = 1) in the presence of a carbonyl compound yields 1 1 adducts 560, whereas homoallyl ester 559 ( = 2) under the same conditions produces only 1 2 adducts 561 (94CB1537). 

The reaction of dichlorocarbene with ketones and diamines results in near quantitative formation of a mixture piperazinones 584 and 585 (80JOC754). As shown in Section III,C,2, piperazine 78 [R = H, R + R = (CH2)s], the minor product of the Rh2(OAc)4-catalyzed decomposition of diazo ester 73, is the result of the dimerization of the intermediate ylide 76 (84JOC113). Tetrahydropyrazines were synthesized through ring expansion of imidazolidines. Thermolysis or photolysis of diazo compounds... 

Rhodium(II) acetate-catalyzed decomposition of diazo ester 677 gives oxacepham 678 via the formation of oxonium ylide 679 and its subsequent fragmentation (91CC1235). 

Ottmann with the following results. They found that a trace of heavy metal catalyzes decomposition of the diazo ester and so heated a mixture of the ester with 20 parts of benzene in a glass insert of an autoclave at 136-140° and so obtained 7-carbo-ethoxynorcaradiene (1) in much improved yield. The ester (I) is converted into the amide (2), which on alkaline hydrolysis undergoes rearrangement to a mixture of four cycloheptatrienecarboxylic acids. Characterization of these acids led to assignment of the structures formulated. 

The first step in the decomposition of nitrosoamides 123) is formation of the diazo ester 125) which fragments to a diazonium ion pair (128)129 The ion pairs thus produced differ from those obtained in the reaction of diazoalkanes with acids. The ratio of ester to ether formed in the decomposition of rV-nitroso-fV-benzhydrylbenz-amides in alcohol is lower than that found in the reaction of diphenyldiazomethane 132) with acids, and in the solvolysis of benzhydryl benzoate (I35)135,136 This effect has been attributed to the intervention of trans-diazo ester in the decomposition of 125) which leads to a greater distance between carbocation and carbox-ylate anion. In the diazoalkane reaction attack of the acid occurs at the electron-rich carbon atom to generate the carboxylate in the immediate vicinity of the incipient carbocation. 

The reverse trend was found for intramolecular cyclopropanation of a-(alkenyloxysilyl)diazo-acetic esters. For the synthesis of methyl 2,2-diisopropyl-3-oxa-2-silabicyclo[4.1.0]heptane-l-carboxylate (7) from methyl diazo[(but-3-enyloxy)diisopropylsilyl]acetate, the thermal procedure gave the best result. In contrast, the lower homologs, 3-oxo-2-silabicyclo[3.1.0]hexanes, were only obtained by photochemical or catalytic decomposition of the corresponding diazo esters (see also Section 1.2.1.10.). 

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%). ... 

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