Carbonyl with diazoalkanes

Transition metal complexes which react with diazoalkanes to yield carbene complexes can be catalysts for diazodecomposition (see Section 4.1). In addition to the requirements mentioned above (free coordination site, electrophi-licity), transition metal complexes can catalyze the decomposition of diazoalkanes if the corresponding carbene complexes are capable of transferring the carbene fragment to a substrate with simultaneous regeneration of the original complex. Metal carbonyls of chromium, iron, cobalt, nickel, molybdenum, and tungsten all catalyze the decomposition of diazomethane [493]. Other related catalysts are (CO)5W=C(OMe)Ph [509], [Cp(CO)2Fe(THF)][BF4] [510,511], and (CO)5Cr(COD) [52,512]. These compounds are sufficiently electrophilic to catalyze the decomposition of weakly nucleophilic, acceptor-substituted diazoalkanes. 

Palladium(II) compounds have unique characteristics suitable for efficient catalysed cyclopropanation of electron-deficient alkenes using diazoalkanes. Neither copper nor rhodium(II) catalysts have shown comparable reactivity with diazoalkanes, although these catalysts are superior to palladium(II) catalysts for cyclopropanation with diazocarbonyl compounds. A few examples of palladium(II) catalysed cyclopropanation of a,fl-unsaturated carbonyl compounds with diazoalkanes are shown in equations 20-242 °. 

While alkyldiazonium salts are unstable, their conjugate bases, diazoalkanes, are stable enough to be prepared and are nucleophilic towards carbonyl compounds. Diazoalkanes are neutral com-poundij having one fewer proton than diazonium salts and are delocalized structures with a central sp nitrogen atom. 

Alkylidenes have been prepared by reduction of alkyli-dynes, by C H oxidative addition from alkyls, and by treatment of unsaturated metal clusters with diazoalkanes. In most instances, the alkylidene adopts a /r2-h coordination mode. However, alkylidenes with heteroatom substituents may also be found in terminal coordination modes. The latter are typically prepared by the Fischer-type carbene route (see Fischer-type Carbene Complexes) (sequential addition of nucleophilic and electrophilic alkylating agents to carbonyl or isocyanide ligands), by condensation of metal fragments with mono- or dimetallic carbene complexes, or by C-H activation of alkylamines. These heteroatom substituted carbenes may also bind in a p3-ri mode, as in (12). 

Two types of products are generally obtained by reaction of ketones with diazoalkanes a homologous carbonyl compound and a small amount of oxirane. The reaction scheme is presented in Eq. 85. 

Reaction with diazoalkanes. Catalytic amounts of nickel carbonyl decompose diazoalkanes to products evidently formed from an intermediate carbene. Use of a large excess of reagent in the presence of ethanol leads to formation of carboxylic acid esters in yields of 20-25%. 

Tricarbonyliron complexes of conjugated trienes react with diazoalkanes at the free (uncom-plexed) double bond. In the synthesis of dimethyl 2-formylcyclopropane-l, 1-dicarboxylate (48), the ceric ion served the double function of catalyzing the deazetization and removing the tricarbonyl iron protecting group. When the optically active iron carbonyl complex was used, the addition of diazomethane gave selectively one diastereomer and this was used to make optically active dimethyl 2-formylcyclopropane-l,1-dicarboxylate (>90% ee). A similar route was employed to make the optically active formyl cyclopropanes 49, precursors to optically active cis- and tran.v-chrysanthemic acids. 

Homologation of carbonyl compounds. The very bulky organoaluminums promote reaction of aldehydes and ketones with diazoalkanes. Aldehydes afford ketones. 

The sites of alkylation are the oxygen atoms of the hydroxyl, carbonyl, and carboxyl groups in lignin. Reactions a and b are selective with diazoalkanes (a) reacting under anhydrous conditions to alkylate, chiefly, the slightly acidic hydroxyl groups (98) of the phenolic, enolic(99-102), and carboxylic (103-107) units to form ethers. The diazoalkane reaction with carboxylic acids only occurs in solvents in which the acid is deprotonated to an enolate anion. The RN reactions are shown in Equation 2. 

Finally, as if to come full circle and again ponder carbonyl electrophiles that served so admirably in asymmetric epoxidation, the well-known Schlotterbeck chain extension of aldehydes by formal C-H insertion with diazoalkanes has been... 

The Wolff rearrangement is well known as a reaction of diazo ketones, i.e. of diazoalkanes with a carbonyl group in a-position. Reaction 34 demonstrates that diazotized aminonaphthols are mesomeric with naphthoquinone diazides (48b) and that they have therefore also the character of quinonoid diazo ketones (see also Section II.C of this chapter). Wolff rearrangements take place also thermally and catalyzed by silver ions. 

The energetic 1,3,4-oxadiazole (22) is synthesized from the reaction of the tetrazole (20) with oxalyl chloride. In this reaction the tetrazole (20) undergoes a reverse cycloaddition with the expulsion of nitrogen and the formation of the 1,3-dipolar diazoalkane (21) which reacts with the carbonyl groups of oxalyl chloride to form the 1,3,4-oxadiazole rings. 

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. 

A practicable strategy to provide access to chiral pyrazolidine-3-carboxylic acid (16) makes use of asymmetric dipolar cycloaddition of diazoalkanes to u,p-unsaturated carboxylic acid derivatives. For this purpose a chiral auxiliary of the alkene component is used, e.g. Op-polzer s1166 1671 (lf )-2,10-camphorsultam.t164l As shown in Scheme 7, by reaction of (tri-methylsilyl)diazomethane (41) with /V-( aery I oy I )cam p h ors u 11 am (42), the AL(4,5-dihy-dropyrazoline-5-carbonyl)camphorsultam (43) is obtained. Reduction of 44 with sodium cyanoborohydride leads to A-(pyrazolidine-3-carbonyl)camphorsultam (45) as the 35-dia-stereoisomer (ee 9 1) in 65 to 80% yields.[164] The camphorsultam 45 is then converted into the methyl ester 46 by reaction with magnesium methylate without racemizationj1641... 

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