Diazo compounds diazoalkanes

In contrast to aromatic diazo compounds, diazoalkanes are less important as large-scale industrial intermediates. Nevertheless, their dediazoniation reactions offer a series of important applications in organic synthesis, since Wolff (1902) discovered the rearrangement of diazo ketones into carboxylic acids (1-3). After... 

Thermal conversion of diazirines to linear diazo compounds was postulated occasionally and proved by indirect methods. The existence of a diazo compound isomeric to diazirine (197) was proved spectroscopically on short thermolysis in DMSO (76JA6416). An intermediate diazoalkane was trapped by reaction with acetic acid, yielding the ester (198) (77JCS(P2)1214). 

In the case of the reaction between 2-diazopropane and diphenyldiacetylene, the reverse (as compared with other diynes) orientation of addition of the first molecule of the diazo compound with a predominant formation of 4-phenylethynylpyrazole is observed. Therefore, it is noteworthy that whereas the regioselectivity of the addition of diazoalkanes to alkenes is well studied audits products have, as a rule, the structure been predicted with respect to electron effects, the problem of orientation... 

Danishefsky s diene 154 DBFOX 232 dendrimers 229 DPT calculations 308 diacetone glucose derived-titanium(IV) 178 diastereoselectivity 216 diazo compounds 242 diazoalkane cycloadditions 278 diazoalkanes 213, 231 (R,R)-4,6-dibenzofurandiyl-2,2 -bis(4-phenylox-azoline) 250... 

Photo-de-diazoniation has found relatively little application in organic synthesis, as is clearly evident from the annual Specialist Periodical Reports on Photochemistry published by the Royal Society of Chemistry. Since the beginning of these reports (1970) they have contained a section on the elimination of nitrogen from diazo compounds, written since 1973 by Reid (1990). In the 1980s (including 1990), at least 90% of each report is concerned with dediazoniations of diazoalkanes and non-quinon-oid diazo ketones, the rest being mainly related to quinone diazides and only occasionally to arenediazonium salts. 

These complexes can be isolated in some cases in others they are generated in situ from appropriate precursors, of which diazo compounds are among the most important. These compounds, including CH2N2 and other diazoalkanes, react with metals or metal salts (copper, palladium, and rhodium are most commonly used) to give the carbene complexes that add CRR to double bonds. Ethyl a-diazoacetate reacts with styrene in the presence of bis(ferrocenyl) bis(imine), for example, to give ethyl 2-phenylcyclopropane-l-carboxylate. Optically active complexes have... 

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. 

Reaction of diazo compounds with a variety of transition metal compounds leads to evolution of nitrogen and formation of products of the same general type as those formed by thermal and photochemical decomposition of diazoalkanes. These transition... 

Carbenes from Sulfonylhydrazones. The second method listed in Scheme 10.8, thermal or photochemical decomposition of salts of arenesulfonylhy-drazones, is actually a variation of the diazoalkane method, since diazo compounds are intermediates. The conditions of the decomposition are usually such that the diazo compound reacts immediately on formation.147 The nature of the solvent plays an important role in the outcome of sulfonylhydrazone decompositions. In protic solvents, the diazoalkane can be diverted to a carbocation by protonation.148 Aprotic solvents favor decomposition via the carbene pathway. 

With calicenes, diazoalkanes were found293 to react in a different manner from other triafulvenes. Thus, dibenzocalicene 497 together with diazomethane gives the product of addition of two moles of the diazo compound 558, which is likely to arise from primary attack of the 1,3-dipole via (3 + 2) cycloaddition to the triafulvene C3/C4 bond (557). 

The activated methylene compound (5 mmol) in PhH or n-C5H,2 (40 ml) is stirred at 25 °C for 15 h with TosN, (0.99 g, 5 mmol), the catalyst (O.l mmol) and aqueous NaOH (3M, 3 ml). The organic phase is separated, washed well with water, dried (Na2S04), and fractionally distilled under reduced pressure to give the diazo compound. (CAUTION the diazoalkanes are potentially explosive.)... 

The normal byproducts formed during the transition metal-catalyzed decomposition of diazoalkanes are carbene dimers and azines [496,1023,1329], These products result from the reaction of carbene complexes with the carbene precursor. Their formation can be suppressed by slow addition (e.g. with a syringe motor) of a dilute solution of the diazo compound to the mixture of substrate and catalyst. Carbene dimerization can, however, also be a synthetically useful process. If, e.g., diazoacetone is treated with 0.1% RuClCpIPPhjij at 65 °C in toluene, cw-3-hexene-2,5-dione is obtained in 81% yield with high stereoselectivity [1038]. 

The second method listed in Table 10.3, thermal or photochemical decomposition of salts of arenesulfonylhydrazones, is actually a variation of the diazoalkane method, since diazo compounds are intermediates. The conditions of the decomposition are usually such... 

Numerous methods to prepare individual classes of aliphatic diazo compounds have been extensively developed. The major strategies for their synthesis involve the alkaline cleavage of N-alkyl-N-nitroso-ureas, -carboxamides and -sulfonamides, dehydrogenation of hydrazones, as well as diazo group transfer from sulfonyl and related azides to active methylene compounds, and electrophilic diazoalkane substitution reactions. These synthetic methods have been comprehensively reviewed (15,16). Useful information on the preparation of selected diazo compounds can be found elsewhere (6,17). 

An interesting preparation of aliphatic diazoalkanes (R R C = N2 R, R = alkyl) involves the photolysis of 2-alkoxy-2,5-dihydro-1,3.4-oxadiazoles (see Scheme 8.49). When the photolysis is carried out in the presence of an appropriate dipolarophUe, the diazo compounds can be intercepted (prior to their further photolysis) by a [3 + 2] cycloaddition reaction (54). As an example, 2-diazopropane was intercepted with A-phenylmaleimide (54) and norbornenes (55) to give the corresponding A -pyrazolines. 

In an earlier survey of the cycloaddition chemistry of diazo compounds with imines (5), it was noted that diazoalkanes react particularly well with both electron-deficient acyclic and strained cyclic imines, such as 27/-azirines, producing... 

The chemistry outlined in Schemes 8.32 and 8.34 illustrates the complexity of reactions that occur between thiocarbonyl compounds and diazo compounds. Heimgartner and co-workers (214-217) observed a similar reactivity pattern when they combined l,3-thiazol-5(477)-thiones (153) with diazoalkanes. When ethyl diazoacetate was used, additional reaction pathways occurred giving rise to a complex mixture of products (218). An interesting aspect of this chemistry involves... 

In contrast to the P=C bond of phosphaalkenes (Section 8.2.2), double bonds between phosphorus and a heteroatom have not been used much as dipolarophiles. Most of the studies reported so far were devoted to the reactivity of the (X )P=N bond of iminophosphanes. Amino(iminophosphanes) react with diazoalkanes to form 4,5-dihydro-3//-l,2,3,4-triazaphospholes or, by N2 loss from the latter, to imino(alkylidene)-X -phosphoranes (5,238). With P-halogeno-(arylimino)phos-phanes 174 and the appropriate diazo compounds, 3//-l,2,3,4-triazaphospholes 175 (167) and 176 (239) (Scheme 8.40) were obtained as the major products after cycloaddition and eliminative aromatization. 

Ketenes rarely produce [3+ 2]-cycloaddition products with diazo compounds. The reaction possibilities are complex, and nitrogen-free products are often obtained (5). Formation of a cyclopropanone represents one possibihty. Along these lines, the synthesis of (Z)-2,3-bis(trialkylsilyl)cyclopropanones and (Z)-2-trialkylsilyl-3-(triethylgermyl)cyclopropanones from diazo(trialkylsilyl)methanes and appropriate silyl- or germylketenes has been reported (256,257). It was found that subsequent reaction of the cyclopropanone with the diazoalkane was not a problem, in contrast to the reaction of diazomethane with the same ketenes. The high cycloaddition reactivity of diazomethylenephosphoranes also extends to heterocumulenes. The compound R2P(C1)=C=N2 (R = N(/-Pr)2) reacts with CS2, PhNCO and PhNCS to give the corresponding 1,2,3-triazole derivative (60). 

Alkoxy-5-diazomethyl-5//-benzocyclopentenes of type 270 undergo an unusual isomerization reaction leading to tetracyclic azo compounds 271 (316,317) (Scheme 8.66). The reaction readily occurs upon chromatographic workup of the diazo compounds that are prepared by electrophilic diazoalkane substitution using benzotropylium salts. The isolated diazo compounds are thermally converted into 271. The isomerization reaction was interpreted as a formal [4 + 3] cycloaddition. Since [47I + 4ti] cycloaddition reactions are thermally disallowed processes, a... 

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