Dediazotization

Linear polyethylene can further also be considered as polymethylene. Althoguh first prepared by the thermal decomposition of diazomethane,243 244 Meerwein should be credited to have prepared it by catalytic polymerization of diazomethane effected by boron compounds (esters, halides, alkyls)245-247 taking place with concomitant dediazotation ... 

Reductive arylation of enones, TiCl3 induces homolytic dediazotization of diazonium salts to produce aryl radicals, which arylate electron-deficient alkenes.1 Example ... 

Kinetic studies of the substitution reaction of 2-chloro-l-methylpyridinium iodide with phenoxides are consistent with the SnAt mechanism, with rate-determining nucleophilic attack.38 The effects of a variety of ring substituents on the reactivities of 2-fluoro- and 2-chloro-pyridines in reactions with sodium ethoxide in ethanol have been examined. The results were discussed in terms of the combination of steric, inductive, and repulsive interactions.39 Substitution in 2,4,6-trihalopyridines normally occurs preferentially at the 4-position. However, the presence of a trialkylsilyl group at the 3-position has been shown to suppress reaction at adjacent positions, allowing substitution at the 6-position.40 Methods have been reported for the introduction and removal of fluorine atoms for polyfluoropyridines. Additional fluorine atoms were introduced by metallation, chlorination, and then fluorodechlorination, while selective removal of fluorine was achieved by reduction with either metals or complex hydrides or alternatively by substitution by hydrazine followed by dehydrogena-tion-dediazotization.41... 

Fig. 14.21. Ring expansion of cyclic ketones via the Tiffe-neau-Demjanov rearrangement. The first step consists of the additions of HCN or nitromethane, respectively, to form either the cyanohydrin or the /J-nitroalcohol, respectively. The vicinal amino alcohol A is formed in the next step by reduction with LiAlH4. TheTiffeneau-Demjanov rearrangement starts after diazota-tion with the dediazotation.

Fig. 11.24. Mechanisms of the photochemically initiated and Ag(I)-catalyzed Wolff rearrangements with formation of the ketocarbene E and/or the ketocarbenoid F by dediazotation of the diazoketene D in the presence of catalytic amounts ofAg(I). E and F are converted into G via a [1 2]-shift of the alkyl group R1. N2 and an excited carbene C are formed in the photochemically initiated reaction. The excited carbene usually relaxes to the normal ketocarbene E, and this carbene E continues to react to give G. The ketocarbene C may on occasion isomerize to B via an oxacyclopropene A. The [l,2-]-shift of B also leads to the ketene G.

Fluorination of alkenes. The reagent adds in the Markownikofl fashion to alkenes to yield alkyl fluorides (35-90% yield). It converts secondary and tertiary alcohols into the corresponding alkyl fluorides. In situ diazotization followed by dediazotization converts a-amino acids into a-fluorocarboxylic acids (38-98% yield). The reagent converts acid chlorides and anhydrides into acid fluorides. ... 

Thermolysis of enantiopure sulfonyl pyrazolines 241 afforded sulfonyl cyclopropanes 242 in a completely stereoselective manner (Scheme 17) <2004OL4945>. Both cyclopropanes 243 and alkylidenecyclopropanes 244, containing one or two chiral carbon atoms, one of them being quaternary, were obtained by hydrogenolysis of the G-S bond and under Julia conditions, respectively. Thermal dediazotization of 3-(l-fluorovinyl)-3-methylpyrazoline 245 at 250°G afforded l-(l-fluorovinyl)-l-methylcyclopropane 246, which was capable of isomerizing further, at 600°G, to... 

Dediazotization. Aryldiazonium ions react at 80° with this sytem to give fluoroarenes. If sodium chloride, bromide, or iodide is added haloarenes are formed in good yield with less than 10% of fluoroarenes. However, the reaction gives unexpected and novel isomer distributions of haloarenes. That is, the halide ion attacks ring positions in addition to the one (Ci) from which N2 is lost. The results are rationalized on the basis of the ambident nature of aryldia-... 

Copper(I) triflate-catalyzed decomposition of diazoacetates 1 leads to silaheterocycles 2, 3, and 4. Vinylcarbenes or vinylcarbene metal complexes may be assumed as reaction intermediates. With copper(I) chloride as catalyst, the dediazotization of 1 leads to the bicyclic fiiran 5, which formally represents the result of an intramolecular [3+2] cycloaddition of an acylcarbene to the C-C triple bond [5]. 

Microfluidks for Biochemical and Chemical Reactions, Fig. 4 Chloro-dediazotization the Sandmeyer reaction... 

Irradiation at X > 375 nm of the two diastereomeric diazo sulfoxides 31a and 31b underwent hetero Wolff rearrangement affording the a-oxo sulfine 34. The carbene 32 has not been deteeted even in traces and the sulfine 34 is proposed to be formed from 31, via dediazotization, hetero Wolff rearrangement and isomerization of domino sequence. ... 

According to theoretical calculations, there is a low-energy pathway for the direct interaction of diazomethane with carbon monoxide [4j. However, experimental results so far show only evidences for two-step pathways. These involve first the dediazotation of the diazoalkanes in thermal, photochemical, or transition metal mediated reactions [5] resulting in free carbenes (Equation 8.2) or transition metal coordinated carbenes (Equation 8.3), which under proper reaction conditions couple in the second step with carbon monoxide (Equation 8.4 or 8.5) to form ketene products. 

The transition metal complex mediated carbonylative dediazotation of diazoalkanes consists of at least two steps shown in Equations 8.3 and 8.5, which can be parts of a catalytic cycle depicted in Scheme 8.1 in a general form [29]. 

Scheme 8.1 Catalytic dediazotation of diazoalkanes and accompanying reactions with electron-rich reagents.

Manganese carbonyl complexes LMn(CO)2(THF) (L=ti -CH3C5H4 or ti -CsHs) were found to be effective in the dediazotation of diazoalkanes and in the formation of stable manganese carbene carbonyl complexes. See for examples reactions 8.23 and 8.24 [47,48]. 

In a slow dediazotation reaction of bis(trifluoromethyl)diazomethane with (Ph2PCH3)2lr(CO)Cl, the iridium carbene complex 14 was formed and isolated in 37% yield (reaction 8.32) [63]. 

The dediazotation reaction of various diazoalkanes (reaction 8.34) was successfully applied in the preparation of stable dinuclear cobalt carbene complexes (16) containing Tj -cydopentadienyl ligands [66-71]. 

Octacarbonyl dicobalt was found to be an effective dediazotation reagent for ethyl diazoacetate. Under ambient conditions, ethoxycarbonylcarbene-bridged dicobalt carbonyl complexes 23 and 24 were isolated from the reaction mixtures in good yields (reactions 8.42 and 8.43). 

The dediazotation reaction of Ph2CN2 or Ph(CF3)CN2 using the rhodium complex 2S gives the corresponding carbene rhodium complexes 26 and 27 in up to 96% yields (reaction 8.50) [82]. 

Despite the fragmentary results known to date, the dediazotation of diazoalkanes coupled with the carbene-carbon monoxide trapping reaction seems to be a promising synthetic path for the preparation of various carboxylic acid derivatives through the ketene intermediate product. Especially the highly effective and selective cobalt-catalyzed examples of the reactions are worth to explore in more detail. 

Heteroaromatic azides often show photochemistry that is very similar to the photochemistry of simple homoaromatic azides. Ring expansion to cycHc ketenimines is observed, if the photolysis is performed at ambient temperature, and triplet nitrenes are formed upon low-temperature irradiation. If a nitrogen atom is placed adjacent to the nitrene center, such as in 2-pyridylnitrene 100, addition generally takes place away from the nitrogen atom. In the case of the photolysis (or pyrolysis) of the 2-azidopyridine 99, the reaction leads to the cycHc carbodiimide 101. A comphcation arises from the fact that derivatives of 2-azidopyridine and related heterocycles frequently undergo a thermal isomerization to tetrazolopyridines, which also undergo photochemical dediazotation, albeit with a low quantum yield. ... 

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