Tosylhydrazones, 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). 

The related borane bis(benzoyloxy)borane has also been found to be effective for tosylhydrazone reductions, examples of which are presented in Table 10 (entries 7 and 8). The latter case required the use of NaOD/D20 for efficient deuterium incorporation (instead of NaOAc/ThO). A pyridine-bo-rane complex likewise reduces tosylhydrazones in acidic ethanol/dioxane to tosylhydrazines (91-98% yields), which may be converted to hydrocarbons by treatment with KOH/MeOH or Na0Ac-3H20/CHCl3. ... 

As with cyanoborohydride, very few functional groups are affected by catechol borane under the tosylhydrazone reduction conditions (25 °C), allowing highly selective conversions in the presence of most moieties, including alkenes and alkynes which are hydroborated at more elevated temperatures (70-100 The only exceptions to this appear to be aldehydes, carboxylates, sulfoxides, amine oxides and anhydrides, which are reduced at rates comparable to tosylhydrazones. ... 

Tosylhydrazone reduction Additive reduction with elimination... 

Tosylhydrazone reduction with elimination Additive reduction 0.038 25.000 0.308 0 0 Isohypsic... 

Two techniques, electrochemical reduction (section IIl-C) and Clem-mensen reduction (section ITI-D), have previously been recommended for the direct reduction of isolated ketones to hydrocarbons. Since the applicability of these methods is limited to compounds which can withstand strongly acidic reaction conditions or to cases where isotope scrambling is not a problem, it is desirable to provide milder alternative procedures. Two of the methods discussed in this section, desulfurization of mercaptal derivatives with deuterated Raney nickel (section IV-A) and metal deuteride reduction of tosylhydrazone derivatives (section IV-B), permit the replacement of a carbonyl oxygen by deuterium under neutral or alkaline conditions. 

Reduction of tosylhydrazone derivatives to the corresponding methylene analogs with metal hydride complexes provides an excellent solution to this problem. Soon after the discovery of this reaction it was recognized... 

Thus, the reduction of tosylhydrazones with sodium borodeuteride in dioxane provides only monodeuterated analogs. For the insertion of two deuteriums it is necessary to first exchange the hydrazone proton and to carry out the reduction in aprotic or deuterated solvents. Under these conditions the reduction of the tosylhydrazone derivatives of 7- and 20-keto... 

Deuteration at C-3 by Lithium Aluminum Deuteride Reduction of 5a.-Pregnane-3,20-dione 3-Tosylhydrazone 20-Ethylene keta ... 

Reduction of Steroidal Tosylhydrazones with Sodium B orodeuteride... 

The following general procedure has been used for the reduction of the tosylhydrazone derivatives of various steroidal ketones. A mixture of the tosylhydrazone (50 mg) and sodium borodeuteride (50 mg) in dry dioxane (3 ml) is heated under reflux for 2 hr, and then the excess deuteride is decomposed by the addition of a few drops of acetic acid. Ether is added and the resulting solution is washed with 2 N sodium bicarbonate solution and... 

The reduction of a,jS-unsaturated ketones to olefins may also be effected via the tosylhydrazones (see section XI-A). 

The reduction of tosylhydrazones by complex metal hydrides has been used very effectively to prepare saturated steroid hydrocarbons in high yields. ... 

Deuteration at C-3 by lithium aluminum deuteride reduction of 5a-pregnane-3, 20-dione 3-tosylhydrazone 20-ethylene ketal, 177... 

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

The nitro group of ct-nitro ketones is readily removed either by treatment v/ith BiuSnH or reduction v/ith LiAlHl of the cotrespondmg tosylhydrazones fEq 3 58 Details of denitration are discussed in Section 7 2, and some applications of this process are shovm in Schemes 35-37... 

The tosylhydrazone is prepared from the carbonyl compound and then reduced with lithium aluminium hydride, sodium borohydride or potassium borohydride. In this way D-glucose tosylhydrazone was converted into crystalline 1-deoxyglucitol by reduction with potassium borohydride... 

The reduction of tosylhydrazones by LiAlH4 or NaBH4 also converts carbonyl groups to methylene.277 It is believed that a diimide is involved, as in the Wolff-Kishner reaction. 

Reduction of tosylhydrazones of a, (3-unsaturated ketones by NaBH3CN gives alkenes with the double bond located between the former carbonyl carbon and the a-carbon.280 This reaction is believed to proceed by an initial conjugate reduction, followed by decomposition of the resulting vinylhydrazine to a vinyldiimide. 

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