Hydrazones diazo compounds from

This section deals with the photochemical loss of nitrogen from compounds containing a diazo group. As a result of the scale of the work some material has had to be excluded. Within this section paths to the synthesis of diazo compounds from hydrazones have been omitted. Much of the use of diazo compounds and the photochemical (and thermal) elimination of nitrogen is in the generation of carbenes, from which a variety of reactions of synthetic value can occur. This short section is aimed mainly at that area, although some reference will be made to the elegant low-temperature studies that have been carried out. 

Mercuric oxide potassium hydroxide Diazo compounds from hydrazones s. 17, 348 19, 354... 

Mercuric oxide/potassium hydroxide Diazo compounds from hydrazones... 

Scheme 20.12 In situ generation of diazo compounds from hydrazones.

A formal ring enlargement of diazirines to five-membered rings is also observed with some hydrazones of ketodiazirines (65CB2509). On attempted preparation of hydrazones (201) from ketodiazirine (200) at 0 C the diazo compounds (202) are plausible intermediates since their transformation to aminotriazoles (203) is known. 

The mechanism of the coupling reaction has been very exhaustively studied. Summarising first what has already been mentioned, it must be noted that the reaction is not confined to the aromatic series, for diazo-compounds condense also with enols and with the very closely related aliphatic aci-nitro-compounds. The final products of these reactions are not azo-compounds, but the isomeric hydrazones formed from them by rearrangement. 

In search of a convenient procedure for preparing diazo substrates for the cycloaddition to Cgg, Wudl introduced the base-induced decomposition of tosyl-hydrazones [116]. This procedure allows the in situ generation of the diazo compoimd without the requirement of its purification prior to addition to Cgg. Since they are rapidly trapped by the fullerene, even unstable diazo compounds can be successfully used in the 1,3-dipolar cycloaddition. In a one-pot reaction the tosyUiydrazone is converted into its anion with bases such as sodium methoxide or butylHfhium, which after decomposition readily adds to Cgg (at about 70 °C). This method was first proven to be successful with substrate 142. Some more reactions that indicate the versatility of this procedure are shown in Table 4.4. Reaction of 142 with CgQ under the previously described conditions and subsequent deprotection of the tert-butyl ester leads to [6,6]-phenyl-C5j-butyric acid (PCBA) that can easily be functionalized by esterification or amide-formation [116]. PCBA was used to obtain the already described binaphthyl-dimer (obtained from 149 by twofold addition) in a DCC-coupling reaction [122]. 

A -1,3,4-Thiadiazoline-1 -oxides (146) (Equation (18)) are formed by addition of diazo compounds (R2C=N2) to sulfines (R R C =S=0). The adducts from diazomethane and aryl substituted sulfines are unstable and give the thiadiazole (147) via a Pummerer-type aromatization <84CHEC-I(4)545>. The A -thiadiazoline-1,1-dioxide (149) has been produced by oxidation of the hydrazone (148) (Equation (19)) and treatment with sulfur dioxide <84CHEC-i(4)545>. 2-Alkylidenethiadiazolines can be obtained from the dipolar addition of diazo compounds to thioketenes <83CB66, 90TL3571, 92HCA1825>. 

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). 

Stable representatives of telluroketones were not available until recently. 2,5-Dihydro-1,3,4-telluradiazole 172 can be prepared from hydrazones 171 and tellurium tetrachloride or tetrabromide in yields of 19-48 and 42-55%, respectively (Scheme 8.39) (237). Ketazines 173 were obtained as byproducts of this reaction in 32 5% yield. It was proposed that XeX4 is hrst reduced to TeX2 in the reaction medium. The latter species probably generates both the diazo compound and the telluroketone derived from hydrazone 3 and then a [3+2] cycloaddition occurs. In fact, both 172 and 173 were obtained when hydrazones 3a-c were treated with the difhcult-to-handle tellurium dichloride in the presence of triethylamine. 

Weiss and co-workersprepared a series of oxazohnylidene steroids 343 as luminescence dyes for application as potential intracellular diagnostic agents (Scheme 6.72). The key intermediate 2-aryl-5,5-dimethyl-4(57/)-thiooxazolones 341 were readily available from the corresponding 4(57/)-oxazolones 339. Reaction of 341 with 342, generated in situ from the hydrazone 340, gave 343 as expected. It was not possible to prepare 343 from 3-thio-androsta-l,4-dien-17-one since the requisite corresponding heterocyclic diazo compounds could not be prepared. 

Another method for the preparation of the 1,2,4,5-tetrazine system from a diazo compound was reported by Staudinger and Meyer (19HCA619). They reacted diaryldiazomethanes (321) with triethylphosphine and isolated the phosphazines (322). In moist benzene or chloroform these compounds were transformed into 3,3,6,6-tetraaryl-l,2,3,6-tetrahydro-1,2,4,5-tetrazines (323). This result was only obtained when triethylphosphine was used. The intermediate formation of hydrazones seems unlikely, since these compounds are stable and do not dimerize. A reaction which has a certain similarity to the above was reported by Merrill and Shechter (75TL4527). They obtained 3,6-diphenyl-l,4-dihydro-l,2,4,5-tetrazine (80) when the phosphazine (324) was hydrolyzed. 

The development of modern organic pigments started with the synthesis of dyestuffs for the textile industry. The period up to 1900 was characterized by the discovery and development of many dyes derived from coal-tar intermediates. Rapid advances in color chemistry were initiated after the discovery of diazo compounds and azo derivatives (shown to be largely hydrazone derivatives). The wide color potential of this class of pigments and their relative ease of preparation led to the development of azo colors, which represent the largest fraction of manufactured organic pigments. 

Acylation of 2- -octylthiochroman by AczO is quantitative at the 6-position (Equation 23) <2003PS(178)993> and benzoylation of thioxanthene occurs at the 2- and 7-positions and both ketone functions have been converted into the hydrazones and thence the diazo compound 277. The bis-carbene derived from 277 by cryogenic photolysis has been used to study magnetic coupling interactions through the sulfur atom (Scheme 32) <1997JA8058>. 

In 2001, a modified procedure for sulfur ylide-catalyzed epoxidation, aziridination and cyclopropanation was introduced by Aggarwal and co-workers that utilized the generation of the diazo compounds in situ from tosyl hydrazone salts at 40 °C in the presence of a phase-transfer catalyst [46, 79]. (For experimental details see Chapter 14.12.1). Using this modified protocol, sulfide 4 was shown to be effective for epoxidation and aziridination (see Sections 10.2.1.4 and 10.3), but was not an effective cyclopropanation catalyst (see Table 10.3). Sulfide 28 was tried instead as it had been shown in achiral studies [96] that six-membered sulfides were more effective than five-membered analogues. This change gave rise to... 

Bis(pyridinio)iodo]benzene triflate is a potent oxidant, as corroborated from polarographic measurements indeed, its E /2 value, +0.34 V, exceeds enormously that of DIB which has only — 1.0 V. For example, it converted hydrazones into diazo compounds and 1,2-bis hydrazones into alkynes, in good to excellent yields ... 

Bis-diazohexane 326 was prepared from the corresponding bis-hydrazone 53 by oxidation with nickel peroxide. Reaction of the bis-diazo compound 326 with elemental sulfur gave the hexahydro-l,2-dithiocin 307 in 77% yield (Equation 24) <2002HAC351>. 

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