Diazomethane addition

However, in the case of a-substituted unsaturated esters (4), as for example methacrylic or tiglic acid esters, diazomethane addition results in the formation of stable A pyrazolines (5). The latter products require halogen acids for conversion to the isomeric nonconjugated A -pyrazolines (6). 

The presence of a 21-acetoxy group is also compatible with good yields during diazomethane addition. ... 

With -3-ketones, i.e., (11), diazomethane addition proceeds with attack at the A -bond leading to stereospecific formation of [2a,la-c]-A -pyrazolines (12). 

In the 6-chloro-A " series diazomethane addition and pyrazoline cleavage require more strenuous conditions. " An unexpected result is observed with the 4-chloro-A system (15) which adds two equivalents of diazomethane to give the 4-chloro-la,2a 6, 7 -dimethylene compound (16) in 16% yield after cleavage of the labile crude bispyrazoline with a catalytic amount of perchloric acid. The assignment of the -configuration to the 6,7-methylene group is based on the shift of the 19-H NMR resonance to higher field. 

The regiospecificity observed above for diazomethane addition is lost when other diazoalkanes are used, for example, dimethyldiazomethane s reaction with 1,1-difluoroallene [24] (equation 16)... 

On the other hand, alkyl substitution on the 1,1-difluoroallene does not affect the regiospecificity of diazomethane addition [24] (equation 17)... 

Charrette and Lebel [24] developed a catalytic enantioselective cyclopropa-nation of trans-cinnamate esters with diazomethane. Their procedure involves an argon-flow-mediated diazomethane addition, leading to high yields (up to 80%) in products with up to 80% ee, by using the bis(oxazoHne) arising from phenylglycinol (Scheme 10). 

Yet another synthesis of a phosphirane derivative (P-CiV = 4) involves diazomethane addition to (132 equation (79)) (75AG(E)363). 

Spiro epoxides are also valuable intermediates for the synthesis of type I branched-chain sugars. These spiro epoxides are formed from ketosugars using diazomethane addition or sulfonium chemistry. Further ring opening of the epoxide allows the introduction of various nucleophiles [1], Chloro spiroepoxide 15 (Scheme 9) has been prepared recently from ketosugar 1 dichloromethyllithium [28]. 

CB2527). The latter are formed in a stepwise manner and are not directly formed from the educts by a simple extrusion of N2. In the first step a fragmentation into thioketones and diazomethane occurs, followed by the generation of methylene from diazomethane. Addition of methylene to the thioketones finally leads to the ylides.3... 

Diazoalkanes, like azides, are 1,3-dipoles of the propargyl-allenyl type (Scheme 87)15 and their reaction with imines provides a route for building the triazoline framework from the C—N—N and C—N fragments. Although diazomethane addition to the carbon-carbon double bond was achieved by von Pechmann in 1898,325 its reaction toward the carbon-nitrogen double bond was investigated only 50 years later. 

Alkylaluminum halides have been investigated as catalysts in the benzalaniline-diazomethane addition.342 Reaction occurs at — 78°C in the presence of diethylaluminum chloride to yield the triazoline adduct diethyl-aluminum iodide, however, leads only to an aziridine. 

Dipolar cycloadditions are characterized by a negative volume of activation,343,344 and diazomethane addition to benzalanilines is accordingly favored by an increase in pressure at 5000 atm high yields of adducts are obtained.345 Pressure facilitates the approach of diazomethane to the double bond of the imine.345... 

Diazomethane addition to arylidenearyloxyanilines in dioxane-water330 fails to give triazoline adducts in the majority of cases.346 Where good yields of products are reported,346 the reaction appears to be facilitated by the ortho substituents on the C-phenyl group331 the failure of the reaction in other cases appears to arise from the electron-releasing mesomeric effect of the 4-phenoxy substituent on the AT-phenyl ring (Scheme 91). 

Triazolines resulting from diazomethane addition to the carbon-nitrogen double bond in oximes decompose rapidly even at 20°C to give N-alkoxyaziridines.361,362... 

Condensation products of aromatic aldehydes and 4-thiohydantoins react with Grignard reagents to give the colorless products 112. Compounds 113 and 114 are formed by alkylation and diazomethane addition reactions.285 These condensation products also react as dienes with acrylonitrile, ethyl acrylate, and other dienophiles giving adducts 115.286... 

The azepino-indole (600 E = COjMe) is produced by thermolysis of methyl 2-azidodiphenylmethane4 -carboxylate, N3C6H4CH2C6H4C02Me. Treatment of the pyrrolo-azepine (601) with benzoylmethylenetriphenyl-phosphorane, PhCOCH=PPh3, yields the bridged compound (602) by successive Michael addition and intramolecular Wittig reaction The imidazo-azepine (604) is formed from (603) by ring-expansion with diazomethane.Addition of dimethyl acetylenedicarboxylate to the cyclo-... 

There are a few reactions of double bonds, such as the addition of CHjCOSH to compound (197) (Equation (65)) <84MI 8ll-0l> and the formation of jpzra-cyclopropanes such as (198) by diazomethane addition (Scheme 17) <89TL3ioi, 92TL5605>. An additional fused pyrimidine ring has been added to compounds (199) by a conventional route (Equation (66)) <89Mi 8ii-04>. 

FIGURE 3.76 Diazomethane addition to give fluorinated pyrazolines and fluorinated cyclopropane. 

Insertion reactions of alkylidene carbenes offer a useful entry to cyclopentene ring systems (4.81). Insertion is most effective with dialkyl-substituted alkylidene carbenes (R = alkyl), since rearrangement of the alkylidene carbene to the alkyne occurs readily when R = H or aryl. A number of methods have been used to access alkylidene carbenes. One of the most convenient uses a ketone and the anion of trimethylsilyl diazomethane. Addition of the anion to the ketone and eUmination gives an intermediate diazoalkene, which loses nitrogen to give the alkylidene carbene. For example, a synthesis of the antibiotic (-)-malyngolide started from the ketone 102 (4.82). The insertion reaction takes place with retention of configuration at the C—H bond. 

Gurana Scarpi et al. in 2000 introduced a modification to this variant which steers away from the use of the diazomethane addition step as shown in the synthesis of 38. Thiolactam 35 is alkylated with ethyl vinyl ketone in the presence of potassium carbonate and 18-crown-6 in tetrahydrofuran (ethyl vinyl ketone is introduced in excess by slow addition over a 2 h period to prevent S-alkylation) to give the AT-alkylated ketone 36 in 97% yield. A thioiminium ion was formed with Me2S04 followed by cyclization with DBU under reflux to give 38 in a good 67% yield. ... 

By Cyclopropanation. 2-Cyclohexenone reacts with diazomethane in the presence of catalytic Pd(OAc)2 to give the expected cyclopropyl ketone (eq 119) and this process represents an especially useful way of preparing such systems. However, when the enone carries an amide unit at the y-carbon, a competing pathway, commencing with diazomethane addition to the carbonyl group, is observed. Under acidic conditions, tetrahydrobenzoxa-zoles are the observed products of reaction (eq 120). ... 

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