Tosylhydrazones, formation reduction

As is the case with Wolff-Kishner reactions, the application of tosylhydrazone reductions relies on the successful conversion of carbonyls to the requisite hydrazone derivatives (58). This usually presents no problem except with relatively hindered or deactivated ketones and, in fact, several failures of the methodology are traced to unsuccessful tosylhydrazone formation (i.e. for examples with 62, 63, -- diketone (9) in equation 4, and the substrate of entry 3, Table 2). 

Reduction of tosylhydrazones (1, 1051 2, 377-378). The Caglioti reduction of tosylhydrazones has been extended to a synthesis of dimethyl alkanephos-phonates (2) from the tosylhydrazones (1). Reduction with sodium borohydride in THF results in formation of (2) reduction in methanol leads to dimethyl... 

Olefin formation by reduction of keto derivatives via tosylhydrazones, 354 Olefin formation by reduction of thioketals, 356... 

The reduction of tosylhydrazones by complex metal hydrides has been used very effectively to prepare saturated steroid hydrocarbons in high yields.317 In certain cases this reduction (with lithium aluminum hydride) takes a different course, and olefins are formed.318 The effect is dependent on both the reagent concentration and the steric environment of the hydrazone.319 Dilute reagent and hindered hydrazone favor olefins borohydride gives the saturated hydrocarbon. The hydrogen picked up in olefin formation comes from solvent, and in full reduction one comes from hydride and the other from solvent. This was shown by deuteriation experiments with the hydrazone (150) 319... 

Tosylhydrazones behave as weak acids on reduction in DMF at a platinum electrode the first peak of fluorenone tosylhydrazone (XXIII) is due to reduction of a proton with formation of the tosylhydrazone anion (XXIV) [83] ... 

For the ring expansion, a particular method has been developed, which became known as the Esdienmoser fragmentation . [178, 179] After a Weitz-Schaefer epoxidation and the formation of a tosylhydrazone, its decomposition is carried out at 0 °C in weakly acidic media (acetic acid diluted with dichloromethane), which contrasts the otherwise similar Wolff-Kishner reduction. 

Synthesis.—Catecholborane offers a number of advantages over other boron hydrides for the reduction of a)3-unsaturated tosylhydrazones (1) to olefins. Only one equivalent of hydride is used and the conditions are mild. No alkane formation is observed. A study of the isomeric pulegone tosylhydrazones (2) and (3) and the... 

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