Tosylhydrazones decomposition

A few related observations deserve comment. The presence of an ii-keto function completely inhibited solvolysis of the I2j0-sulphonates by its opposed inductive effect, but did not prevent the tosylhydrazone decomposition and rearrangement [1087. This may be a reflection of the exceptionally low activation energy for the decomposition of an aliphatic diazo-nium ion into a carbonium ion and molecular nitrogen (p. 316). Rather surprisingly, the Cps) cyanohydrin (15) undergoes similar rearrangement on dehydration with thionyl chloride/ pyridine [108,11 ]. 

The second method in Scheme 9.1, thermal or photochemical decomposition of salts of arenesulfonylhydrazones, is actually a variation on the diazoalkane method, since diazo compounds are intermediates. It is an important and useful method, however, since the ultimate starting materials are ketones, and also because the procedure avoids isolation of the potentially dangerous diazoalkanes. The conditions of the decomposition are usually such that the diazo compound reacts soon after formation, and high concentrations do not build up. The nature of the solvent mixture plays an important role in the outcome of tosylhydrazone decompositions. In the presence of proton donors, the diazoalkane intermediates can be... 

The Bamford-Stevens decomposition of tosylhydrazones by base has been applied to steroids, although not extensively. It has been demonstrated that the reaction proceeds via a diazo compound which undergoes rapid decomposition. The course of this decomposition depends upon the conditions in proton-donating solvents the reaction has the characteristics of a process involving carbonium ions, and olefins are formed, often accompanied by Wagner-Meerwein-type rearrangement. In aprotic solvents the diazo compound appears to give carbene intermediates which form olefins and insertion products ... 

Reduction of tosylhydrazones of a, (3-unsaturated ketones by NaBH3CN gives alkenes with the double bond located between the former carbonyl carbon and the a-carbon.280 This reaction is believed to proceed by an initial conjugate reduction, followed by decomposition of the resulting vinylhydrazine to a vinyldiimide. 

The most common rearrangement reaction of alkyl carbenes is the shift of hydrogen, generating an alkene. This mode of stabilization predominates to the exclusion of most intermolecular reactions of aliphatic carbenes and often competes with intramolecular insertion reactions. For example, the carbene generated by decomposition of the tosylhydrazone of 2-methylcyclohexanone gives mainly 1- and 3-methylcyclohexene rather than the intramolecular insertion product. 

Compound 34 can be synthesized by a Bamford-Stevens procedure from compound 33. Loer explored the cyclization of 32 with polyphosphoric acid (PPA), followed by decomposition of the tosylhydrazone to form the desired 177-2,1-benzothiazine 2,2-dioxide 34 in good overall yield (Scheme 8) <66JOC3531>. 

The thermochemistry of 4,4-diphenylcyclohexa-2,5-dienylidene (lu) in solution was investigated by Freeman and Pugh (Scheme 19).106 The thermal decomposition of the diazo compound 2u (produced in situ from the corresponding tosylhydrazone lithium salt) produces a complex product mixture with the azine as the major product (51%). Volatile monomeric products biphenyl and several terphenyls were also formed in low yields. 

Attempts to prepare 2-diazo-3-oxindole failed. In fact, base decomposition of the isatin-2-tosylhydrazone under conventional conditions with potassium hydroxide at room temperature led to the potassium salt (64JOC3577). When an aqueous solution of the potassium salt was heated at 70°C, indigo blue was obtained in 62% yield. 

Bicyclobutane has been prepared by intramolecular addition of a divalent carbon to an olefinic double bond,1 2 irradiation of butadiene,3 decomposition of cyclopropanecarboxaldehyde tosylhydrazone,4 and deamination of cyclobutylamine and cyclopropylcarbinylamine.5 The present procedure is based upon a published method.6 This procedure gives the highest yield of the known methods and provides a process for making moderate quantities of material. 

An exceptionally interesting example of an intramolecular [3 + 2] cycloaddition, in which the diazo dipole and the olefinic C=C bond are separated by only one carbon atom, is outlined in Scheme 8.65. The thermal decomposition of the allenic tosylhydrazone sodium salt 267 produced 1,4-dihydropyridazine 269 (57). It is assumed that diazabicyclohexene 268 is a short lived reaction intermediate. This suggestion is supported by the observation that the generation of the diazocumulene l-diazo-2-methyl-l-propene in the presence of 3,3-dimethylcyclopropene also leads to 269. 

This is a major route of decomposition of ethyl 2-furyldiazoacetate (%) (R = H, = C02Et) when heated in dichloromethane or methanol (74JOC2939). The same type of decomposition has been observed with other 2-furylcarbenes which were generated by decomposition of the sodium salts of tosylhydrazones at 3(X)°C (78JA7927). Thermolysis of the diazo compound 96 (R = R = H) in cyclooctane or styrene gave, besides the open-chain acetylene 97, products of intermolecular carbene insertion. This led the authors to favor the carbene mechanism of ring-opening (path A in Scheme 7). 

Thermal decomposition of y-lactone tosylhydrazone sodium salts are reported to yield cyclobu-tanones, which can be accounted for by rearrangement of an intermediate oxycarbene. In this manner, the sodium salts of dihydrofuran-2(37/)-one tosylhydrazones 1 were decomposed as a loose powder, at 310 C in a bulb-to-bulb distillation apparatus at an initial pressure of 0.1 Torr, to give the corresponding cyclobutanones 2 in addition to enol ethers, cyclopropanes and open-chain alkenes. Condensable products (74-76%) were collected at — 78 °C, weighed and the ratio of components was determined from their relative GC peak areas.63... 

Carbenes are known intermediates in the thermolytic or photolytic decomposition of the lithium or sodium salts of tosylhydrazones, which, for endocyclic carbenes, results in ring contraction when the elimination of / - or y-hydrogens is impeded. Simple cyclobutanes generally cannot be prepared by this route from monocyclic cyclopentanone tosylhydrazones. However, the lithium salt of bicyclo[2.2.1]heptan-7-one tosylhydrazone gave bicyclo[3.2.0]hept-l-ene (4) as the major product (74%) by vacuum pyrolysis at 185 JC/20 Torr, together with bicyclo[2.2.1]heptane (14%) and tricyclo[2.2.1.02,7]heptane (12%) in 80% overall yield.67... 

Since the first report in 1960 of the observation that sodium methoxide induced carbenoid decomposition of cyclobutanone tosylhydrazone (1) at 180 °C in either bis(2-ethoxyethyl) ether or /V-methylpyrrolidone results in an intriguing ring contraction to produce methylenecyclopropane (3),1 many experimental results have been presented invoking cyclobutylidene (2) as a key intermediate in this rearrangement. 

Homofulvenes 8 (4-alkylidenebicyclo[3.1.0]hex-2-enes <25%), in addition to several hydrocarbon products (10-35%), are formed in the thermal decomposition of sodium salts of bicyclo[3.2.0]hept-2-en-6-one tosylhydrazones 5 at 130-150°C in both protic and aprotic solvents.8 The formation of homofulvenes 8 may be explained by the initial conventional ring contraction of the cyclobutylidenes 6 to the methylenecyclopropanes 7, the strain of which is released in a thermal rebonding to give homofulvenes 8.8... 

The major limitation of the vacuum pyrolysis method appears to be thermal decomposition of less volatile diazo compounds during the pyrolysis. The vacuum pyrolysis method was unsuccessful for the preparation of 1-naphthyl diazomethane and 3,5-dichlorophenyldiazomethane. However, such diazo compounds could be prepared from the corresponding tosylhydrazone salts by pyrolysi s in ethylene glycol and extraction of the aryldiazomethane into... 

Carbenes of type (367), generated by thermal decomposition of the appropriate tosylhydrazone salts, undergo ring opening more readily when the ring heteroatom is oxygen than when it is sulfur... 

Diazomethane and its simple analogs undergo cycloaddition to unsaturated compounds both directly and after conversion to carbenes. The direct cycloadditions are 1,3-dipolar for the most part and provide access to pyrazolines and pyrazoles. Intramolecular cyclizations were recognized as early as 1965 95 The two main methods used in generation of diazo compounds for subsequent intramolecular cycloaddition include thermolysis of tosylhydrazone salts and thermolysis of iminoaziridines. Decomposition of nitros-amines has also been employed. 

Silylcarbenes, especially when generated by photochemical or thermal decomposition of diazo compounds or tosylhydrazone alkali salts or a-hydroxy-a-silylsilanes, tend to... 

An alternative procedure is to convert the carbonyl compound into the toluene-p-sulphonylhydrazone,12 followed by reduction with either sodium borohydride in acetic acid,13 or with catecholborane, followed by decomposition of the intermediate with sodium acetate or tetrabutylammonium acetate.14 The former method is illustrated by the conversion of undecan-6-one into undecane (Expt 5.6), and the latter by the conversion of acetophenone into ethylbenzene (Expt 6.4, Method B). A feature of these methods is that with a, / -unsaturated ketones, migration of the carbon-carbon multiple bond occurs thus the tosylhydrazone of isophorone gives 3,3,5-trimethylcyclohex-l-ene, and the tosylhydrazone of oct-3-yn-2-one gives octa-2,3-diene. 

The problem of distinguishing between carbenoid and carbonium ion mechanisms of decomposition of diazoalkanes in protic media arises also in interpreting the base-induced decomposition of tosylhydrazones. In the original procedure for this widely-used reaction (W. R. Bamford and Stevens, 1952), the tosylhydrazone of a carbonyl compound is treated with the sodium salt of ethylene glycol in refluxing glycol. A mixture of olefins and alkoxyethanol is produced (equation 6). Many... 

Fig. 17.71. Reduction of a conjugated tosylhydrazone. Since the diazene intermediate D cannot decompose via a diazene anion (cf. Figure 17.67-17.69) for lack of base and the radical decomposition mechanism of Figure 17.70 is not employed either, the third of a total of three mechanisms of the diazene —> hydrocarbon transformation is presented here.

Diazo-l, 8-, 3,6-, and 4,5-diazafluorenes are obtained by alkaline decomposition of the respective 9-tosylhydrazones. Photolysis of these diazo compounds yields reactive carbenes whose properties and reactions were investigated by Schuster and Li <86JOC3806, 87JOC3975) and by Durr and coworkers <89TL1935>. 

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