Reactions Bamford-Stevens

The Bamford-Stevens reaction and the Shapiro reaction share a similar mechanistic pathway. The former uses a base such as Na, NaOMe, LiH, NaH, NaNHa, heat, etc., whereas the latter employs bases such as alkyllithiums and Grignard reagents. As a result, the Bamford-Stevens reaction furnishes more-substituted olefins as the thermodynamic products, while the Shapiro reaction generally affords less-substituted olefins as the kinetic products. 

Bamford, W. R. Stevens, T. S. M. J. Chem. Soc. 1952, 4735. Thomas Stevens (1900-2000), a chemist centenarian, was bom in Renfrew, Scotland. He and his student W. R. Bamford published this paper at the University of Sheffield, UK. Stevens also contributed to another name reaction, the McFadyen—Stevens reaction (page 354). 

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

The starting material A aziridinyl imine is also known as Eschenmoser hydrazone. 

Name Reactions, 4th ed., DOI 10.1007/978-3-642-01053-8 8, Springer-Verlag Berlin Heidelberg 2009 

Name Reactions A Collection of Detailed Mechanisms and Synthetic Applications, DOI 10.1007/978-3-319-03979-4 8, Springer International Publishing Switzerland 2014 

Example 5, Diazoesters from aiylsulfonylhydrazones by means of m-flow Bamford-Stevens reactions 

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. 

The titled reaction was first reported by William Randall Bamford and Thomas Stevens Stevens in 1952 at The University of Sheffield. It is closely related to the Shapiro reaction, in which tosylhydrazones are treated with alkyl lithium reagents to form alkenes. This valuable transformation has received extensive attention, as testified by the references cited herein. 

The mechanism was originally proposed by Powell and Whiting, with further corroboration by others soon thereafter. The first step of the Bamford-Stevens reaction is the formation of the diazo compound 3, via the tosylate salt 2.  

The mechanism for alkene formation was found to be dependent upon the reaction conditions. For instance, in protic media, the diazo compound 3 can be protonated to form a diazonium ion 5, resulting in the formation of a carbocation 6 upon loss of dinitrogen. 

This pathway does not occur in the absence of protons, and in aprotic media, dinitrogen loss results in the formation of carbene intermediates 8. 

The Bamford-Stevens synthesis is related to the Shapiro reaction (Shapiro and Heath, 1967 reviews Shapiro, 1976 Adlington and Barrett, 1983), in which a 4-toluenesulfonyl hydrazone of an aldehyde or a ketone is treated with at least two equivalents of a very strong base, usually, methyllithium (see Organic Syntheses examples of Chamberlin et al., 1983, and Shapiro et al., 1988). The Shapiro reaction leads to an olefin by a hydrogen shift. The mechanism has been proposed by Casanova and Waegell (1975) as given in (2-34). This mechanism involves a diazenide anion 2.81 as intermediate. 

For the Bamford-Stevens reaction, smaller amounts of methyllithium or other bases, such as sodium alcoholates, LiH, NaH, sodium ethylene glycolate, or NaNH2 are used. The consequence is that the C — H group adjacent to the hydrazone moiety does not dissociate (2-35). Padwa et al. (1983 b) applied a similar process (2-36, NaH in THF) for the synthesis of the diazoalkene 2.82. 

The problem concerning the neighboring CH group does not exist in the Bamford — Stevens reaction of 2,2,4,4-tetramethylpentan-3-on -toluenesulfonylhy-drazone (2.83), which gives di( A butyl)diazomethane (2 4), with sodium hydride in tetrahydrofuran in 90% yield (Barton et al., 1974) (2-37). 

Depending on the solvent used, the reaction often does not stop (or is not stopped by intention) at the diazoalkane stage, but goes on to carbenes or to carbocations. Carbenes and their reaction products (olefins) are formed in apolar systems, carbocations and subsequently, their stable products in protic solvents (2-38). 

2 Methods for the Preparation of Alkane, Athene, and Alkyne Diazo Compounds 

The electron-donating hydroxy substituent is necessary in order to facilitate the migration of the aryl group otherwise a substituted benzoic acid would be obtained as reaction product. 

Harwood, Polar Rearrangements, Oxford University Press, Oxford, 1992, p. 53-59. 

Reaction of tosyl hydrazone 1 with a strong base initially leads to a diazo compound 3, which in some cases can be isolated  

Depending on the reaction conditions, the further reaction can follow either one of two pathways which lead to different products. 

In a protic solvent—glycols are often used, with the base being the corresponding sodium glycolate—the reaction proceeds via formation of a carbenium ion 5. The diazo compound 3 can be converted into the diazonium ion 4 through transfer of a proton from the solvent (S-H). Subsequent loss of nitrogen then leads to the carbenium ion 5  

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Okfm Syntheses. Conversion of aldehydes and ketones to olefins by the base-catalyzed decomposition of -toluenesulfonic (Ts) acid hydrazones (10) is known as the Bamford-Stevens reaction (54,55). 

The alkyl lithium method gives high yields of -olefins from 17-ketones via the tosylhydrazones. A -Olefins are formed from 6- and 7-ketones. (Compare with the Bamford-Stevens reaction which gives A - and A -olefins, respectively.) In the presence of an excess of alkyl lithium, alkylation may occur. 

Baeyer-Villager oxidation, 10, 151, 433 Bamford-Stevens reaction, 402 Barton reaction, 253 Beckmann rearrangement, 140 Benzilic acid rearrangement, 418, 435 3 -Benzoyloxy-7-methylenecholest-5-ene, 60 Benzylmagnesium chloride, 64 3-Benzyloxycholesta-3,5-diene, 342... 

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 ... 

An unusual synthesis of the l,6-dihydro-l,2,3-triazine system 8 involves the Bamford-Stevens reaction of cis-aziridinylketone tosylhydrazones 7 in the presence of a "slight excess" of sodium hydride or sodium ethoxide. If a large excess of sodium ethoxide is used then isopropylamino-3,5-diaiylpyrazoles are formed <%H(43)1759>. 

The l,3-dithian-2-ylidene substituted carbene (54), accessible from the tosylhydrazone (53) by a Bamford - Stevens reaction, not only participates in cycloaddition reactions but is also a source of 4,8-dithiaspiro[2.5]oct-l-ene 6JCS(P1)2773>. 

Phosphoryl-substituted diazo compounds of general type 4 have recently been synthesized by amine diazotization, Bamford-Stevens reaction, and diazo group... 

The most frequent synthetic approaches, summarized in Scheme 4, are towards the primary photophores. The preparation of aryl azide derivatives follows the typical retro-synthetic pathway in the majority of the reported cases (Scheme 4 A), and, practically, diazotation is the most commonly used procedure [24 - 29]. In the case of diazirines only one major synthetic sequence is repeated ammonolysis of oximes followed by dehydrogenation (Scheme 4B) [30-32]. There are various ways of preparing diazo- or diazocarbonyl-compounds most frequently the Forster and Bamford-Stevens reactions (Scheme 4C) are employed [33-37]. 

Baeyer-Villiger reaction, 9, 3 43, 3 Bamford-Stevens reaction, 23, 3 Barbier Reaction, 58, 2 Bart reaction, 2, 10 Barton fragmentation reaction, 48, 2 Bechamp reaction, 2, 10 Beckmann rearrangement, 11, 1 35, 1 Benzils, reduction of, 4, 5 Benzoin condensation, 4, 5 Benzoquinones ... 

Cycloadditions to [6,6]-double bonds of Cjq are among the most important reactions in fullerene chemistry. For a second attack to a [6,6]-bond of a C q monoadduct nine different sites are available (Figure 10.1). For bisadducts with different but symmetrical addends nine regioisomeric bisadducts are, in principle, possible. If only one type of symmetrical addends is allowed, eight different regioisomers can be considered, since attack to both e - and e"-positions leads to the same product. Two successive cycloadditions mostly represent the fundamental case and form the basis for the regioselectivity of multiple additions. In a comprehensive study of bisadduct formations with two identical as well as with two different addends, nucleophilic cyclopropanations, Bamford-Stevens reactions with dimethoxybenzo-phenone-tosylhydrazone and nitrene additions have been analyzed in detail (Scheme 10.1) [3, 9, 10]. 

The product hydrazide may be sulfonated and decomposed by heating with a base in ethylene glycol to yield benzaldehyde, CeHsCHO. Many aromatic aldehydes may be produced by similar routes. The hydrazone derivative of toluenesulfonic acid reacts with an aldehyde or a ketone in the presence of a base catalyst, such as sodium ethoxide, to yield the corresponding olefin (Bamford-Stevens reaction) ... 

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