Thermal Bamford-Stevens

No increased C H insertion into methyl group. In contrast to all other reaction conditions, trace amounts of insertion product 30 are produced only by the thermal Bamford-Stevens method in high-boiling NMP.111 Formation of bis (2-methylcyclohexanylidene)hydrazine (31) is inhibited in MeOH, due to the short... 

The starting material A -aziiidinyl imine is also known as Eschenmoser hydrazone. Example 2, Thermal Bamford-Stevens ... 

Support-bound sulfonylhydrazones can also be used as linkers for alkenes. Cleavage is effected by heating in the presence of an alcoholate, whereby diazoalkanes are initially formed these then undergo thermal fragmentation into the alkene and nitrogen (Entry 12, Table 3.43 Bamford-Stevens reaction). Polystyrene-bound alkynyl... 

Activation by silicon of a P-C-H bond to an intramolecular carbene insertion reaction is exemplified by the silicon-directed Bamford-Stevens reaction.68 For example, thermal decomposition of P-trimethylsilyl /V-aziridinyl imines 72 in toluene (Scheme 8) [with or without Rh2(OAc)4 catalyst] results in the formation of allylic silanes 73 as major or exclusive products by the preferential insertion of the carbene intermediate into the C-H bond P to the silicon substituent. 

The parent 3-piperideine (3) was prepared from l-acetyl-4-piperi-done by conversion into the p-toluenesulfonylhydrazone and thermal fission of the latter in alkaline media (the Bamford-Stevens reac-... 

Mechanistic information on the photolytic Bamford-Stevens reaction is provided by the successful isolation of a diazo hydrocarbon as a reaction intermediate from the direct photolysis of a tosylhydrazone sodium salt (90 Scheme 10). This study also clarifies that the carbene derived thermally and that derived photolytically behave differently with respect to the stereoselectivity of the 1,2-hydrogen shift that produces the alkene. 

Olmstead, K. K., Nickon, A. 1,2-Hydrogen shifts in thermal and photic Bamford-Stevens reactions of cyclohexanones. Activation by an endocyclic oxygen. Tetrahedron 1998, 54,12161-12172. 

As masked diazo compounds the salts of tosyl hydrazones can react thermally and photochemically ( Bamford-Stevens-reaction ) to give alkenes (Scheme 3, variable... 

Additional data on the thermal rearrangement of cnrfo-cineole halohydrins and dihalides to halopinol derivatives (Vol. 8, p. 44) have been reported. ° In further attempts to synthesize 2,3-didehydro-l,8-cineole, nitrosation of the endo- and exo-aminocineoles (157) results in a stereospecificity not observed with dehydration of the corresponding alcohols (Vol. 8, p. 41) endo- 51) yields (158) and exo- 51) yields (159). The successful route to 2,3-didehydro-1,8-cineole involves reduction of 2-hydroxyimino-l,8-cineole with sodium bis-(2-methoxyethoxy)aluminium hydride to the corresponding aziridine followed by nitrosation interestingly, LiAlH4 reduction of 2-hydroxyimino-l,8-cineole is the most efficient route for the synthesis of (160). Bamford-Stevens reaction. 

Carbenes produced by photolysis of diazoalkanes are highly energetic species and often react indiscriminately. Thermal decomposition of diazoalkanes can be catalysed by certain transition metal (particularly copper or rhodium) salts, to produce less energetic and more selective carbenes. The active species in such a reaction is thought to be the metallocarbene rather than the free carbene. Another convenient and widely used route to alkylcarbenes is the thermal or photolytic decomposition of the lithium or sodium salts of toluene-p-sulfonylhydrazones. The diazoalkane is first formed (by elimination of the toluenesulfinate anion) and decomposes imder the reaction conditions to give the carbene (4.76). This process is often referred to as the Bamford-Stevens reaction. 

Most commonly, photolytic, thermal, or transition metal catalyzed decomposition of diazoalkanes is used to create carbene molecules. A variation on catalyzed decomposition of diazoalkanes is the Bamford-Stevens reaction, which gives carbenes in aprotic solvents and carbenium ions in protic solvents. Another method is induced elimination of halogen from gem-dihalides or HX from a CHXj moiety, employing organoHthium reagents (or another strong base). It is not certain that in these reactions actual free carbenes are formed. In some cases there is evidence that completely free carbene is never present instead, it is likely that a metal-carbene complex forms. Nevertheless, these metallocarbenes (or carbenoids) give the expected products. 

Example 1, Tandem Bamford-Stevens/thermal aliphatic Claisen rearrangement... 

The synthesis of sulfones has been performed by iron-catalysed decomposition of sulfonylhydrazones. As commonly accepted for the related Bamford Stevens reaction, the reaction is thought to proceed through generation of a diazocompound by base-mediated thermal decomposition of the sulfonylhydrazone, leading to an intermediate iron carbenoid (65), which forms the sulfone (66) when trapped by the sulflnate anion released in the first step (Scheme 9). 

Bamford-Stevens and Shapiro Reactions. Thermal decomposition of the monoanions of arenesulfonylhydrazones in aprotic... 

Bamford-Stevens and Shapiro Reactions. The Bamford-Stevens reaction is used to obtain unsaturated compounds from tosylhydrazones. A base is required to generate its monoanion, which thermally decomposes to yield the corresponding di-azo derivatives. These reactive species evolve to give an aUcene through carbenium ions in protic solvents or carbenes in aprotic solvents. The thermal decomposition of the monoanions of trisyl-hydrazones is commonly used to obtain diazoalkanes for different applications such as functionalization of solid supports, epox-idation and alkenylation of aldehydes, or the study of radicals and carbenes The functionalization of a Merrifield resin with... 

The Bamford-Stevens reaction is the formation of an alkene 4 by the treatment of the tosylhydrazone 1, of an aldehyde or a ketone, with a base. A few diazo compounds 3 can be isolated if mild temperatures are employed however in the majority of cases, the diazo compounds thermally decompose to form alkenes. 

Nickon investigated the 1,2-hydrogen shifts in thermal and photic Bamford-Stevens reactions of cyclohexanones. Under eonditions known to favor the Shapiro reaction, tosylhydrazone 18a afforded the two expected alkenes 19 and 20 as well as an unexpected product (identified as 21) in a ratio of 15 60 25. Under conditions known to favor the Bamford-Stevens reaction, lithium salt 18b was subjected to thermolysis (neat, 170 °C) and also to photolysis (pentane suspension, -70 °C). Under both sets of conditions the three products 19, 20 and 21 were formed in approximately the same ratio (84 4 12 and 83 6 11), thus demonstrating the switching of major alkene product from 19 to 20 on moving from the Shapiro reaction to the Bamford-Stevens reaction. 

The development of a tandem rhodium-catalyzed Bamford-Stevens/thermal aliphatic Claisen rearrangement sequence was elegantly demonstrated by Stoltz. As a general method to prepare non-carbonyl-stabilized diazo compounds in situ, this group chose to investigate the decomposition of //-aziridinyl imines (also known as Eschenmoser hydrazones) 28. ... 

In the early 1950s Bamford and Stevens reported a thermally induced reaction of ketone tosylhydra-zone monosodium salts that gives products derived either from carbene intermediates (aptotic conditions) or carbocations (protic conditions). Both reactions, which are illustrated in Scheme 51, can give alkenes as the major product, although the protic reaction is of marginal synthetic value because mixtures of alkene regioisomers and rearrangement products are normally obtained. On the other hand, the... 

The base-mediated conversion of arylsulfonylhydrazones to alkenes was first observed by Bamford and Stevens in 1952.6 In a representative transformation, tosylhydrazone 3 was converted to cyclohexene (4) in quantitative yield after refluxing for 90 minutes in an alkoxide solution derived from dissolution of sodium in ethylene glycol. These reactions are believed to proceed via intermediate diazo compounds, which are transformed to alkenes by thermal elimination processes. 

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