Diazoalkanes from tosylhydrazones

The cycloaddition of diazoalkanes to alkynes gives pyrazoles the use of stannyl alkynes ° produces tin derivatives of the heterocycle (cf. 4.1.6), for use in subsquent electrophilic ipio-displacements, or in palladium(0)-catalysed couplings. Aryl-diazomethanes can be generated in situ, from tosylhydrazones, for formation of pyrazoles. ... 

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... 

Many more carbenes can be made safely from diazoalkanes if the diazoalkane is just an intermediate in the reaction and not the starting material. Good starting materials for these reactions are tosylhydrazones, which produce transient diazo compoimds by base-catalysed elimination of toluenesulfinate. The diazo compound is not normally isolated, and decomposes to the carbene on heating. 

Not all vinylcarbenes will cyclize to the cyclopropene. For example, those with an acyl substituent on the carbene-bearing center preferentially undergo a Wolff rearrangement, but the most significant limitations to the scope of this synthetic route arise from the problems of making the required 3//-pyrazoles. Many routes exist, but as far as cyclopropene synthesis is concerned, the 3/f-pyrazoles have been made (1) by addition of diazoalkanes to alkynes (2) from dihydropyrazoles (3) from cyclization of a,/l-unsaturated tosylhydrazones and finally (4) by modification of the structure of other 37/-pyrazoles. 

On treatment of series of a-tosylhydrazonophosphonates with aqueous sodium carbonate, they underwent facile Bamford-Stevens-type elimination to give the corresponding diazoalkanes (equation 132) with the exception of the tosylhydrazone derived from 4-chlorobutyrylphosphonate, which underwent cyclization (equation 133) . ... 

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