By the Bamford-Stevens reaction

A non-Kekule molecule, a /n-xylylene (88), has been generated by the Bamford-Stevens reaction of a fulvene-ketene adduct (85), via the homofulvene (87) from the intermediate carbene (86). This unstable intermediate readily dimerizes to octamethyl[2.2]metacyclophane (89 Scheme 9). ... 

Chen s stereospecific total synthesis of cycloeudesmol 48 started with the hydrazone 46, which was converted to the allylic alcohol 47 by the Bamford-Stevens reaction followed by DMF trapping of the vinyl anion and sodium borohydride reduction. This allylic alcohol 47 was then taken on through a further ten steps to yield the natural product cycloeudesmol 48. 

X = NO2) with triethyl phosphite or by heating the azide (229 X = N3) was not successful, but phenothiazine analogues were obtained by the Bamford-Stevens reaction with (229 X = CH=NNHTos). ... 

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). 

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 ... 

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>. 

The intermediate bicyclo[2,2,l]heptyl cation has been written in Fig. 1 in its unbridged form by analogy with conclusions reached from studies of the Bamford-Stevens reaction of 18 stereospecifically deuteriated in either the 6-exo- or 6-endo positions (Nickon and Werstiuk, 1966). Under aprotic conditions (diglyme/sodium methoxide), the product is entirely norticyclene (19), formed without loss of deuterium in keeping with carbene formation followed by intramolecular insertion. Under standard protic conditions, 19 still constitutes more than 90% of the reaction product, but 19% of the label is lost from ea o-deuteriated starting material and 52% from the endo-deuteriated compound,... 

The reduction of a carbonyl group to an olefin has been accomplished by the Shapiro modification5 of the Bamford-Stevens reaction and by the hydride reduction of the corresponding enol ether,6 enol acetate,7 or en-amine.8 The nickel reduction of the thioketal has also been used successfully.9... 

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. 

Solid-state photolyses were conducted in argon-purged borosilicate flasks. After 2 h, no more diazirine 26 was present by NMR nor by gas chromatographic (GC) analysis. The results of solution photolyses of diazirine 26 are shown in Table 3. Carbene 27 can also be generated from the 2-methylcyclohexanone p-tosyl hydra-zone sodium salt (33) via the Bamford-Stevens reaction.116 The gas phase results are also included in Table 3 as are the results of Wilt and Wagner.111... 

Loev and co-workers152 prepared the unsubstituted lH-2,l-benzothia-zine 2,2-dioxide (239) by the route of Scheme 11. Methyl chlorosulfonyl-acetate was converted into the sulfonanilide (235) by reaction with aniline. Hydrolysis of the ester group in 235 gave 236 which, with polyphosphoric acid, cyclized to 1 H-2,l-benzothiazin-4-one (237). Spectral data indicated that 237 existed in the keto form. Ketone 237 was converted to the tosylhydra-zone 238 which, by a Bamford-Stevens reaction, afforded 239 in good overall yield. The iV-methyl analog of 239 was also prepared by the above reaction sequence using N-methylaniline. 

The first successful syntheses of phosphorus-containing diazoalkyl compounds (1) appear to have been reported independently by two groups of workers. Petzold and Henning employed a method presently described as that of diazo transfer, in which an active methylene compound, as its anion, is treated with an aromatic sulphonyl azide. Seyferth et al on the other hand, reported on a development to the Bamford-Stevens reaction, in which a carbonyl/7-toluenesulphonylhydrazone is treated with a base. Both methods thus depend on modifications to compounds with existing phosphorus-carbon bonds, as do other procedures which have since been developed. 

The Bamford-Stevens reaction is frequently used not for the isolation of aliphatic diazo compounds, but for the synthesis of the products obtained by dediazoniation either by the carbene or the carbocation mechanisms in (2-38). As 4-toluenesulfonyl-hydrazones are fairly stable under Bamford-Stevens conditions, the reactions must be carried out at higher temperature, which is, of course, a disadvantage when it is desired to stop the reaction at the diazoalkane stage. Yields above 90% can, however, be obtained in some cases, particularly for the synthesis of 9-diazofluorene (Dudman and Reese, 1982). 

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). 

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. 

Cleavage of a, -unsaturated p-tosyUiydrazones. Reaction of an a,)9-un-saliirated p-tosylhydrazone with sodium borohydride and methanol affords an allylic or benzylic methyl ether rather than a hydrocarbon as shown in the examples. Actually NaBH4 can be replaced by sodium methoxide or potassium carhoualc. The reaction is probably related to the Bamford-Stevens reaction. ... 

Much more widely used carbene precursors are tosylhydrazones, which are readily prepared from aldehydes or ketones by reaction with 4-toluenesulfonyl hydrazide. Tosylhydrazones produce transient diazo compounds by base-catalyzed elimination of toluenesulfinate. The diazo compound is not normally isolated, and decomposes to the carbene on heating. The whole process is known as the Bamford-Stevens reaction. The leaving group is not the famihar tosylate (toluene-p-sulfonate, p.CH3-C, H4S03 , TsO ), but the less famihar toluene-p-sulfinate (Ts , P.CH3-C5H4S02 ) (Scheme 5.7). 

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