Alkenes Bamford-Stevens reaction

From 5 the formation of alkene 2 is possible through loss of a proton. However, carbenium ions can easily undergo a Wagner-Meerwein rearrangement, and the corresponding rearrangement products may be thus obtained. In case of the Bamford-Stevens reaction under protic conditions, the yield of non-rearranged olefins may be low, which is why this reaction is applied only if other methods (e.g. dehydration of alcohols under acidic conditions) are not practicable. 

A more promising procedure for the formation of alkenes from tosylhydrazones is represented by the Shapiro reaction It differs from the Bamford-Stevens reaction by the use of an organolithium compound (e.g. methyl lithium) as a strongly basic reagent ... 

In the related Bamford-Stevens Reaction, thermodynamic bases are used and the more substituted alkene is formed. 

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... 

The Shapiro Reaction, a variation on the Bamford-Stevens Reaction, is the base-induced reaction of tosylhydrazones to afford alkenes. This reaction is carried out with two equivalents of an organolithium compound. 

The Bamford-Stevens reaction is a tosylhydrazones, 4.106, decomposition with a base to form alkenes. 

Mechanism The first step of the Bamford-Stevens reaction is the formation of the diazo compound A by the treatment of tosylhydrazone with a base. The reaction mechanism involves a carbene B in an aprotic solvent (Path A) and carbocation C in a protic solvent (Path B) (Scheme 4.53). When an aprotic solvent is used, predominantly Z-alkenes are obtained, while a protic solvent gives a mixture of E- and Z-alkenes. If there is a choice of product, the more substituted alkene is produced predominantly. 

Finally, hindered arenesulfonylhydrazones can undergo addition of the alkyllithium rather than deprotonation, and, in fact, the normal Shapiro conditions generally do not give any alkene if an a-methine proton must be removed in the initial deprotonation step. Shapiro reported that the use of LDA overcomes the problem,but there are later examples in which this modification is ineffective. In one such case, lithium t-butylamide proved to be superior (Scheme 72) and in another it proved necessary to re-son to the aforementioned N-aminoaziridine derivative in an aprotic Bamford-Stevens reaction, when the normal Shapiro and Bamford-Stevens conditions failed (Scheme 73). ... 

The reaction also takes place with other bases (e.g., LiH, Na in ethylene glycol, NaH, NaNH2) or with smaller amounts of RLi, but in these cases side reactions are common and the orientation of the double bond is in the other direction (to give the more highly substituted alkene). The reaction with Na in ethylene glycol is called the Bamford-Stevens reaction For these reactions two mechanisms are possible a carbenoid and a carbocation mechanism. The side reactions found are those expected of carbenes and carbocations. In general, the carbocation mechanism is chiefly found in protic solvents and the carbenoid mechanism in aprotic solvents. Both routes involve formation of a diazo compound (35) which in some cases can be isolated. 

The Bamford-Stevens reaction is the base-catalyzed decomposition of arenesulfonylhydrazones of aldehydes and ketones, leading to the formation of alkenes an or cyclopropanes. There are several important general reviews in this area of organic synthesis. Since the reactions are mostly carried out either in protic or in aprotic solvents, the reaction types are divided into the protic and aprotic Bamford-Stevens processes. This section reviews recent examples in the synthesis of alkenes and cyclopropanes from arenesulfonylhydrazones, which is closely related to the following Shapiro reaction. 

The protic Bamford-Stevens reaction has been successfully utilized in the asymmetric synthesis of the naturally occurring sesquiterpenes (+)-a-eudesmol and (-)-a-selinene. Here, the more-substituted alkene was formed preferentially (equation 4,1). ... 

The aprotic Bamford-Stevens reaction has been utilized for the development of a methodology towards 1,2-carbonyl transposition in natural product synthesis. The example in Scheme 8 illustrates the regiocontrolled alkene formation for the synthesis of hirsutic acid. ... 

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. 

The Bamford-Stevens reaction is particularly effective for the generation of 9-phenyl-l(9)-homo-cubene (93), the most twisted alkene yet known. Thus, thermolysis of the cubyl phenyl ketone tosylhydrazone (91) in ethanolic sodium ethoxide or photolysis of the diazo compound (92) in ethanol both give good conversions to a 3 2 mixture of the isomeric ethers (95) and (96) (Scheme 11). The formation of (96) suggests the intervention of l-phenyl-9-homocubylidene (94) via the rearrangement of (93). 

The reaction of tosylhydrazones with sodium in ethylene glycol to give alkenes had been observed before (Bamford-Stevens reaction) other bases, e.g. NaOMe, alkali metal hydrides and NaNH2 were also used. However, in these cases side reactions occur and, in contrast to the Shapiro reaction, the more highly substituted alkene is predominantly formed. Two mechanisms are discussed for these reactions a mechanism via a carbenium ion, which usually takes place in protic solvents, and a carbene mechanism in aprotic solvents (Scheme 28). In both cases diazo compounds are intermediates, which can sometimes be isolated. ... 

The base catalyzed decomposition of arylsulfonylhydrazones of aldehydes and ketones to provide alkenes is called the Bamford-Stevens reaction. When an organolithium compound is used as the base, the reaction is termed the Shapiro reaction. The most synthetically useful protocol involves treatment of the substrate with at least two equivalents of an organolithium compound (usually MeLi or BuLi) in ether, hexane, or tetramethylenediamine. The in s/ft formed alkenyllithium is then protonated to give the alkene. The above procedure provides good yields of alkenes without side reactions and where there is a choice, the less highly substituted alkene is predominantly formed. Under these reaction conditions tosylhydrazones of a,(3-unsaturated ketones give rise to conjugated dienes. It is also possible to trap the alkenyllithium with electrophiles other than a proton. 

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

The first traceless linker was developed by Kamogawa and coworkers in 1983 [82]. Starting from a polymer-bound sulfonylhydrazine, sulfonylhydrazone resin 88 was formed by reaction with ketones or aldehydes. The cleavage step was conducted either by reduction with sodium borohydride or lithium aluminium hydride to yield alkanes 89 or by treatment with base to give the corresponding alkenes 90 in a Bamford-Stevens reaction (Scheme 16.20). This work was a pioneering approach in the field of traceless tinkers. 

Ketone 4-toluenesulfonylhydrazone salts can be used for carbene formation. The mild thermolysis and the photolysis of these salts leading to diazoalkanes are known as the Bamford-Stevens reaction. If run under more energetic conditions, the metastable diazoalkanes form carbenes and their subsequent products (e.g., alkenes), or, in the presence of mild acids, products of carbocations (see Subsect. 2.5.2). 

Bamford-Stevens reaction. Tosylhydrazones undergo the Bamford-Stevens reaction in a two-phase system (aqueous NaOH-dioxane) to give diazo compounds. Depending on the structure, the diazo compounds can be isolated or converted into alkenes or products of cyclization or cycloaddition. ... 

Hydrazones can be readily prepared by the addition of a hydrazine to an aldehyde or ketone. Treatment of tosyl hydrazones (or other arylsulfonyl hydrazones) with a base has been used for the preparation of alkenes. In the Bamford-Stevens reaction, a mild base, such as NaOMe or KH, is employed and promotes deprotonation of the acidic N—H proton (compare with the Eschenmoser fragmentation. Scheme 2.33). 

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