Toluene-p-sulphonylhydrazones

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. 

To a slurry of undecan-6-one toluene-p-sulphonylhydrazone (5.08 g, 15 mmol) (1) in 50 ml of glacial acetic acid is added sodium borohydride pellets (c. 5.67 g, 150 mmol, 24 pellets) (2) at such a rate that foaming is not a problem (c. 1 hour). The solution is stirred at room temperature for 1 hour and then at 70 °C for 1.5 hours. The solution is then poured into crushed ice, made basic with aqueous sodium hydroxide and extracted with three portions of pentane. The pentane solution is dried and concentrated in a rotary evaporator, and the residue distilled at reduced pressure (Kugelrohr apparatus) to obtain 1.96 g (84%) of undecane. Undecane has b.p. 87 °C/20 mmHg. 

An alternative milder procedure is the reduction of the corresponding toluene-p-sulphonylhydrazones with catecholborane, followed by decomposition of the intermediate with sodium acetate in the presence of dimethyl sulphoxide, or with tetrabutylammonium acetate.1 These methods, which do not have the disadvantages of the Clemmensen reduction, are illustrated by the preparation of ethylbenzene from acetophenone (Expt 6.4, Methods A and B). Outline mechanisms for these reactions are given below. 

Method B. The toluene-p-sulphonylhydrazone of acetophenone (0.721 g, 2.5 mmol) (1), m.p. 140—141.5 °C, is placed in a flame-dried, nitrogen-filled flask containing 5 ml of chloroform. Catecholborane (0.52 ml, 5.0 mmol) (Section 4.2.7, p. 420) is added and the reduction allowed to proceed for 2 hours at room temperature (2). Methanol (1 ml) is added to destroy the excess of hydride followed by the addition of tetrabutylammonium acetate (0.7 g, 2.5 mmol). The reaction mixture is stirred for 4 hours when g.l.c. analysis indicates a 94 per cent yield of ethylbenzene. The product is isolated by distillation, yield 0.21 g (79%), b.p. 132-136 °C. 

Notes. (1) The general procedure for the preparation of toluene-p-sulphonylhydrazones is given in Expt 5.6. 

Toluene-p-sulphonylhydrazones of the Pentose Sugars, with Particular Reference to the Characterisation and Determination of Ribose, D. G. Easterby, L. Hough, and J. K. N. Jones,/. Chem. Soc., (1951) 3416-3418. 

A cyclopentane aldehyde (297) is obtained when verbenone epoxide (298) is treated with zinc bromide. The presence of pinene in the products is difficult to explain, and the difference in products obtained with aluminium chloride (Vol. 1, p. 45) is remarkable. When the toluene-p-sulphonylhydrazone of the epoxide (298) is treated with potassium t-butoxide, both isomers of the cyclobutyl-acetylene (299) are obtained in an Eschenmoser fragmentation. ... 

Photodecomposition of sodium salts of toluene-p-sulphonylhydrazones is a well-established route for the generation of carbenes. Irradiation of the lithium salt of the hydrazone (150) or the diazoalkenyl ether (151) derived from it afforded... 

Tetraphenyldiazocyclopentadiene has been prepared by the action of alkali on the toluene-p-sulphonylhydrazone of tetraphenylcyclopenta-dienone, [57,61], while 2,3,4-triphenyldiazocyclopentadiene is very easily prepared from a triphenyleyelopentenolone, itself very readily obtained [53] ... 

Hydroboration of imines of cyclohex-2-enones has also been investigated. Regiospecificity in olefin formation from toluene-p-sulphonylhydrazones and methyl-lithium is clearly seen. Thus the anti-hydrazone (44) gave the diene (45a) whereas the syn-hydrazone gave a mixture of (45a) and (45b). Several solvent systems were investigated but results showed that the hydrazone stereochemistry had a consistent effect, and that syn anti isomerism was not in operation. 

The optical purities obtained were generally low (<40%). The acid-catalysed reaction of 6-deoxy-l,2-0-isopropylidene-3-0-methyl-a-D-xy/o-hexofuranos-5-ulose 5-(toluene-p-sulphonylhydrazone) (433) with methyl phenylphosphonite has been used in a novel method for the synthesis D-gluco- and L-ido-pyranose derivatives containing a phosphorus atmn in the hemiacetal ring (Scheme 78). ... 

An analogous sequence of reactions with methyl 2,3-dideoxy-(lS)-pentopyranosid-4-ulose 4-(toluene-p-sulphonylhydrazone) (434) afforded l,5-di-0-acetyl-2,3,4-trideoxy-4-C-(phenylphosphinyl)-DL-gfiycero-pentofuranose (435). The Abramov reaction of 2,3 5,6-di-O-isopropylidene-a-D-mannofuranose with dimethyl phosphite yielded the oxaphosphorinane (436) by intramolecular transesterification. ° ... 

The generation of carbenes by reaction of metastable singlet carbon atoms with aldehydes and ketones has been described in detail the distribution of intramolecular rearrangement products is identical with that observed from toluene-p-sulphonylhydrazone-derived carbenes. Suitably substituted carbenes generated in this manner, e.g. that prepared from (4), can be trapped by olefins, when the cyclopropane (5) produced retains the original olefin geometry, indicative of a singlet species. 

The first representative of a new type of helical structure (419), having features of both helicenes and cyclophanes, has been formed by pyrolysis of a sulphone made from the bis(bromomethyl)-quaterphenyl (420a) and the corresponding dithiol (420b). An intramolecular carbene-insertion reaction involving the helicene skeleton has been reported in which l-formyl-[6]helicene toluene-p-sulphonylhydrazone (421) is converted into (422), the structure of which has been determined unambiguously by H and n.m.r. spectroscopy. 

Thiiranium ylides have been posulated as intermediates in the photolysis of S-methyl diazothioacetate (79) and in the thermolysis or photolysis of salts of a-arylthio- and a-alkylthio-toluene-p-sulphonylhydrazones (80). In the latter case the ylides were trapped with diethyl maleate and dimethyl... 

Tricyclic thietanium ions were considered as intermediates in the photorearrangements of methylisothiazoles and in the rearrangements of dihydro-1,4-thiazihe (162). No evidence was obtained for a thietan ylide in the decomposition of sodium salts of toluene-p-sulphonylhydrazones of cyclic sulphides. ... 

---