Benzyl thioenol ethers

The striking effect of the catalyst is exemplified by the reaction of pregna-4, 16-diene-3,20-dione (10) with benzyl mercaptan. In the presence of piperidine only conjugate addition occurs to give (11) whereas with pyridine hydrochloride only the 3-benzyl thioenol ether (12) is formed. In the presence of p-toluenesulphonic acid both reactions take place to yield (13). 

Bamford-Stevens decomposition of tosylhy-drazones, 351 p-Benzoquinone, 308 Benzyl ether hydrogenolysis, 139 Benzyl thioenol ethers, 87 Birch reduction, 11, 49, 50 Birch reduction of estrone methyl ether diethyl ketal, 51... 

Cyanohydrins are formed selectively from saturated as against oc, 3-unsaturated ketones [113], and in the steroid field a further distinction can be made between Cs-ketones and C2o ketones by choice of suitable conditions [198]. Base-catalyzed exchange with acetone cyanohydrin is conveniently employed for their formation [198,199]. In the presence of this grouping which is quite stable to mildly acidic conditions, firee (x, unsaturated ketone groups can be converted into dienol ethers, benzyl thioenol ethers, and dioxolans by conventional methods [113], and saturated ketones can be brominated [200]. Cleavage of this group occurs under very mildly basic conditions such as in ethanol in the presence of pyridine [113]. An additional modification is provided by further conversion into cyanohydrin tetrahydropyranyl ethers which are more base-stable [199]. 

The A" -3-keto group can be selectively protected as a thioenol ether in the presence of a 17- or 20-ketone. High yields are obtained with benzyl mercaptan and pyridine hydrochloride as a catalyst. 

Methyl-l,3-dioxolanyl Enol Acetate, 529 Pyrrolidinyl Enamine, 530 Benzyl Enol Ether, 530 Butyl Thioenol Ether, 530 Protection of Tetronic Acids, 530... 

N-Methyl-N -benzyl thiourea may be obtained by the interaetion of benzylamine and methyl iso-thioeyanate, which on methylation yields a thioenol ether. Displaeement of the eorresponding thiomethyl group by methylamine via an addition elimination process affords bethanidine whieh on treatment with an aliquot of sulphuric acid gives the official product. 

Other condensing agents which have proved useful under certain conditions are boron tiifluoride, formic acid with p-toluenesulphonic acid and hydrochloric acid in acetic add. One unusual example of a thioenol ether formed from a saturated ketone has been reported using hydrogen chloride as the catalyst. In this case, compound 96 was converted to either its benzylthioenol ether 97 or its ethylthioenol ether 98 (equation 79). Benzyl mercaptan normally seems to be the reagent of choice in most conversions because of its easily crystallized products. 

A soln. of 3-acetylamino-l-methyl-4-benzylthio-5-benzylthiomethyl-3-pyrrolin-2-one and diloranil in benzene refluxed 0.5 hr. 3-acetylamino-l-methyl-4-benzyl-thio-5-benzylthiomethylene-3-pyrrolin-2-one. Y 82%. F. e., also with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone, s. K. Hagio and N. Yoneda, Chem. Ind. 1974, 494 thiophenes from 2,5-dihydrothiophenes s. J. M. McIntosh and H. Khalil, Can. J. Chem. 53, 209 (1975) thioenol- from thio-ethers with sulfuryl chloride s. S. Iriudiijima et al., Agr. Biol. Chem. (Tokyo) 40, 1031 (1976). 

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