Aryl diazomethanes

The Lewis acid-Lewis base interaction outlined in Scheme 43 also explains the formation of alkylrhodium complexes 414 from iodorhodium(III) meso-tetraphenyl-porphyrin 409 and various diazo compounds (Scheme 42)398), It seems reasonable to assume that intermediates 418 or 419 (corresponding to 415 and 417 in Scheme 43) are trapped by an added nucleophile in the reaction with ethyl diazoacetate, and that similar intermediates, by proton loss, give rise to vinylrhodium complexes from ethyl 2-diazopropionate or dimethyl diazosuccinate. As the rhodium porphyrin 409 is also an efficient catalyst for cyclopropanation of olefins with ethyl diazoacetate 87,1°°), stj bene formation from aryl diazomethanes 358 and carbene insertion into aliphatic C—H bonds 287, intermediates 418 or 419 are likely to be part of the mechanistic scheme of these reactions, too. 

Phenyldiazomethane, 1, 834. A new method for preparation of this (and other aryl-diazomethanes) involves a vacuum pyrolysis of the sodium salt of benzaldehyde tosylhydrazone, a method introduced for carrying out the Bamford-Stevens reaction. The yield is 80%, the highest yield yet reported. Another advantage is that the reagent is obtained free from solvents. The pyrolysis can also be coitducted in ethylene glycol at 80° with extraction of the aryldiazomethane into hexane.1 Caution All diazo compounds arc highly toxic and potentially explosive. 

Aryl diazomethanes vary in stability. They are formed when diazirines are irradiated and will be be discussed below. 

Zimmerman and Somasekhara demonstrated that benzalazine decomposed thermally by the following mechanism, which involves participation of an aryl-diazomethane intermediate as the chain transfer species, viz. 

Aryl diazomethanes and ethyl diazoacetate lose nitrogen completely when hydrogenated over palladium in neutral medium at room temperature and atmospheric pressure. Aryl diazoketones, however, under the same conditions, give the a-amino ketones which condense directly to the dihydropyrazines. The addition of acetic acid to the solvent for this later reaction permits the isolation of the amino ketone (Eqn. 19.32). With dilute hydrochlorie acid in the reaction mixture, complete loss of the nitrogen was observed. The hydrogenation of alkyl diazoketones in neutral or acetic acid solution results in hydrazone formation (Eqn. 19.33). ... 

In spite of these limitations, a large number of arylcyclopropanes have been synthesized by the addition of arylcarbenes to alkenes. The most versatile synthetic methods involve treatment of benzylic halides with a strong base, and thermal or photochemical decomposition of aryl-diazomethane derivatives. In special cases, less general methods have also turned out to be useful. 

Reaction of Arylcarbenes with 1,1-DimethyIallene by Direct Irradiation of the Corresponding Aryl-diazomethanes Generai Procedure ... 

The cycloaddition of diazoalkanes to alkynes gives pyrazoles the use of stannyl alkynes ° produces tin derivatives of the heterocycle (cf. 4.1.6), for use in subsquent electrophilic ipio-displacements, or in palladium(0)-catalysed couplings. Aryl-diazomethanes can be generated in situ, from tosylhydrazones, for formation of pyrazoles. ... 

It has been shown that aryl diazomethanes can give oxetans upon reaction with chloranil although, as expected, stilbenes are the major products. The oxetans were formed in up to 30% yield depending upon substrate and solvent, and it has been proposed that the reaction proceeds via the intermediate (48). 

The reaction is of wide scope (R = alkyl, aryl) however the substrate molecule should not contain other functional groups that can react with diazomethane. With unsaturated acyl halides the yield can be poor, but may be improved by modified reaction conditions. ... 

Sulfonylureas are not directly amenable to gas chromatography (GC) because of their extremely low volatility and thermal instability. GC has been used in conjunction with diazomethane derivatization, pentafluorobenzyl bromide derivatization, and hydrolysis followed by analysis of the aryl sulfonamides. These approaches have not become widely accepted, owing to poor performance for the entire family of sulfonylureas. Capillary electrophoresis (CE) has been evaluated for water analysis and soil analysis. The low injection volumes required in CE may not yield the required sensitivity for certain applications. Enzyme immunoassay has been reported for chlorsulfuron and triasulfuron, with a limit of detection (LOD) ranging from 20 to 100 ng kg (ppt) in soil and water. 

Carbenes from Diazo Compounds. Decomposition of diazo compounds to form carbenes is a quite general reaction that is applicable to diazomethane and other diazoalkanes, diazoalkenes, and diazo compounds with aryl and acyl substituents. The main restrictions on this method are the limitations on synthesis and limited stability of the diazo compounds. The smaller diazoalkanes are toxic and potentially explosive, and they are usually prepared immediately before use. The most general synthetic routes involve base-catalyzed decomposition of V-nitroso derivatives of amides, ureas, or sulfonamides, as illustrated by several reactions used for the preparation of diazomethane. 

Modifications at the carboxyl group include reduction (with dibor-ane260 or borohydride, after activation with soluble carbodiimide261,262), esterification (with diazomethane,101,223,283,264 or acyl or aryl chlorides224,264), and formation of amide esters.263,265... 

Bis(pinacolato)diboron reacts with diazomethane in the presence of Pt(PPh3)4 to give bis(pinacolatoboryl)methane in 82% yield (Equation (16)).67 Under similar conditions, aryl-substituted diazomethanes (R1 or R2 = Ar) give the corresponding 1,1-diborylalkanes in good yields.75... 

In arylcarbenes not only the internal bond angle but also the dihedral angle between the bond plane and the aryl plane can be bent. Photolysis of a- and /S-naphthyl-diazomethanes in a matrix gave two isomeric carbenes, which produced different ESR signals >. 

Most electrophilic carbene complexes with hydrogen at Cjj will undergo fast 1,2-proton migration with subsequent elimination of the metal and formation of an alkene. For this reason, transition metal-catalyzed cyclopropanations with non-acceptor-substituted diazoalkanes have mainly been limited to the use of diazomethane, aryl-, and diaryldiazomethanes (Tables 3.4 and 3.5). 

When 2-alkyl-3-keto esters or 2-aryl-3-keto esters are treated with sulfonyl azides under basic conditions, nucleophilic deacylation occurs to yield 2-alkyl/aryl-2-diazo esters [960-963]. Nucleophilic deacylation can also be used to convert acceptor-substituted diazoketones into the corresponding acceptor-substituted diazomethanes [964,965]. In all these deacylation reactions it is the most electrophilic carbonyl group which is attacked by the nucleophile and cleaved off. 

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