Sulfonylhydrazones Tosylhydrazones

The problem necessitating the use of excess n-BuLi, and consequently an excess of the electrophile, was obviated by using ketone-derived 2,4,6-triisopropylbenzene-sulfonylhydrazones (trisylhydrazones). Elimination to give the carbanion intermediate is much faster with the trisylhydrazone-derived dianion than with that obtained from tosylhydrazones, presumably because of relief of strain. This shortens the time of exposure of the carbanion to the solvent, thereby reducing the chance of its protonation before it can be trapped by an electrophilic reagent. 

Mesitylene-2-sulfonylhydrazone is found to be particularly effective in the Eschenmoser fragmentation reaction. For example, reaction of the epoxy ketone of type (97) gives rise to the corresponding cy-cloalkynone in reasonable yield (equation 51). The same reaction with tosylhydrazone failed, however. 

The a-alkylation of sulfonylhydrazone dianions with disulfides followed by Shapiro reaction has been used to effect the 1,2-transposition of carbonyl groups.19,20 As shown below, treatment of tosylhydrazone 31 with n-BuLi/TMEDA followed by addition of dimethyl disulfide and deprotonation with an additional equivalent of w-BuLi provided vinylsulfide 32.19 Exposure of this compound to mercuric chloride in hot aqueous acetonitrile provided ketone 33 in 75% overall yield. 

Most tosylhydrazone sodium salts could be usually Isolated from the reaction of the corresponding tosylhydrazones with sodium methoxide. However, a number of more functionalized hydrazone sodium salts, such as those derived from alkenyl aryl (25) sulfonyUiydrazones, ketone sulfonylhydrazones, and trimethylsi-lylacrolein sulfonylhydrazones, could not be isolated and an in situ salt generation procedure using NaHMDS was developed. A mixture of the desired hydrazones and NaHMDS was stirred at —78 °C then concentrated down before the addition of rhodium... 

In particular, sulfonylhydrazones are valuable coupling partners in Pd-catalyzed cross-coupling reactions with aryl halides and pseudohalides giving rise to alkenes. As an example, the reaction of a chloroarene with the tosylhydrazone derived from 4-tert-butylcyclohexanone leads to an aryl substituted cyclohexenone (Experimental Procedure below). " " Moreover, the reaction can be conducted directly from the carbonyl... 

Sulfonylhydrazones having a-hydrogens react with 2 or more equivalents alkyllithium to give olefins. - E 3,3-Dimethyl-2-butanone tosylhydrazone with butyl-lithium at 70-90° in < 1 min. 3,3-dimethyl-1-butene. Y ca. 100%. F. e. s. 

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