Sodium borohydride tosylhydrazones

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 the preformed tosylhydrazones with sodium borohydride may be effected in aprotic solvents, such as tetrahydrofuran or dioxane. The use of lithium aluminium hydride in nonhydroxylic solvents permits the reduction of aromatic aldehydes and ketones. 

In keto steroids the reductions were also achieved by electrolysis in 10% sulfuric acid and dioxane using a divided cell with lead electrodes (yields 85-97%) [862], hy specially activated zinc dust in anhydrous solvent (ether or acetic anhydride saturated with hydrogen chloride) (yields 50-87%) [155, 86J], and by the above mentioned reduction of tosylhydrazones with sodium borohydride (yields 60-75%) [811]. 

The reduction of tosylhydrazones can also be performed with sodium borodeuteride in boiling methanol or dioxane, but the mechanism of this reaction (in boiling dioxane at least) is radically different from that of the lithium aluminum deuteride reductions.82 With sodium borohydride the first step is apparently hydride attack on the carbon atom of the C=N bond which is probably concerted with the elimination of the tosylate anion (110 - 111). Migration of the hydrogen from nitrogen to C-3 in (111) concerted with expulsion of nitrogen, provides the corresponding methylene derivative (100).82... 

An alternative procedure is to convert the carbonyl compound into the toluene-p-sulphonylhydrazone,12 followed by reduction with either sodium borohydride in acetic acid,13 or with catecholborane, followed by decomposition of the intermediate with sodium acetate or tetrabutylammonium acetate.14 The former method is illustrated by the conversion of undecan-6-one into undecane (Expt 5.6), and the latter by the conversion of acetophenone into ethylbenzene (Expt 6.4, Method B). A feature of these methods is that with a, / -unsaturated ketones, migration of the carbon-carbon multiple bond occurs thus the tosylhydrazone of isophorone gives 3,3,5-trimethylcyclohex-l-ene, and the tosylhydrazone of oct-3-yn-2-one gives octa-2,3-diene. 

The tosylhydrazone 20, derived from methyl 2,3-( -isopropylidene-/ -D-ribopyranoside, on treatment with dimethyl phosphite, gives a diastereomeric mixture of 4-dimethoxyphosphinyl-4-tosylhydrazosugars 21 in a 15 85 ratio50. When each epimer alone is reduced with sodium borohydride in tetrahydrofuran, the same mixture of diastereomers of 22 is formed which is due to epimerization at C-4 during the reduction. 

Table 6 Reduction of Carbonyl Tosylhydrazones with Sodium Borohydride...

Rosini, G., Baccolini, G., and Cacchi, S., Reactions of 1-oxoalkanephosphonate tosylhydrazones with sodium borohydride. New synthesis of dimethyl alkanephosphonates and dimethyl 1-diazoalkane-phosphonates. Synthesis, 44, 1975. 

Reduction of tosylhydrazones. Caglioti (Univ. di Bologna, Italy) introduced a simple method for the deoxygenation of aliphatic aldehydes and ketones under mild and neutral conditions consisting in reaction of the tosylhydrazone with sodium borohydride in methanol.35,36... 

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... 

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. ... 

Reductive deoxygenation of most a, -unsaturated tosylhydrazones with NaBHsCN cleanly affords alkenes in which the double bond migrates to the former tosylhydrazone carbon (eq 20). However, the process gives mixtures of alkenes and alkanes with cyclohexenones (see also Bis(triphenylphosphine)copper(I) Borohydride, Catecholborane and Sodium Borohydride). 

A very useful variant of the hydrazone reduction is the deoxygenation of aldehydes and ketones via the hydride reduction of tosylhydrazones (Caglioti reaction) The method is mild, convenient and widely applicable. While sodium borohydride was used in the earlier procedures, considerable improvements have been achieved through the uses of sodium cyanoborohydride, catecholborane, diborane, his-benzoyloxy borane and copper borohydride as reducing agents and HMPA, DMF, sulpholane, etc. as solvents. Use of the sterically crowded 2,4,6-triisopropyl tosylhydrazone derivative has greatly facilitated the reduction in some cases (equations 61-64). ... 

R. O. Hutchins and N. R. Natale. Sodium borohydride in acetic acid. A convenient system for the reductive deoxygenation of carbonyl tosylhydrazones. J. Org. Ghent., 1978, 43, 2299. 

The reaction of tosylhydrazones of a -unsaturated enones with sodium boro-hydride in alcoholic solution leads not to reduction, but instead to elimination according to Scheme 35, to provide a synthesis of allyl ethers in good yields. Potassium carbonate or sodium alkoxides can replace borohydride as the base in this sequence. trans-A y ethyl ethers (74) may be synthesized stereoselectively by the addition of aluminium hydrides to 1-alkynes and subsequent reaction of the vinyl alane formed (Scheme 36). This route complements the same authors ... 

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