Ethylene thioacetals

Dimethyl acetals.2 Nafion-H is recommended as catalyst for the synthesis of dimethyl acetals and ethylene thioacetals. It is also useful for hydrolysis of dimethyl acetals. 

Alternatively, the diester (597) may be oxidised with osmium tetroxide-sodium metaperiodate to the keto-ester (598) which, after reduction of the ketone function by desulphuration of its ethylene thioacetal to give (599), is cyclised and decarboxylated to the unsubstituted ketone (600). 

Cyclization of the dimethyl ester afforded ketone 45, which, by way of the crystalline 8a,9a-epoxide, was converted to the 8, 9a-diol 46. The corresponding diacetate, via the ethylene thioacetal, was deoxygenated to give 47. The 8/1,9/1-epoxide 48, accessible from 47, after treatment with LiAlH4 and oxidation of the resulting hydroxy compound, finally furnished relay ketone 19. 

Reaction of the flavanone (5) to give (6) presumably involves an a-iodo ketone which undergoes elimination (eq 2). The ethylene thioacetal of cyclohexanone gives cyclohexanone (eq 3), and phosphine sulfides and selenides give the 0x0 analogs (eq 4). ... 

Ring-opening of epoxides " and thioacetalization of carbonyl compounds, including amides, are among the reactions reported for (EtS)3B. Cyclic ethylene thioacetals are prepared from the borane precursor in yields usually superior to those for HSC2H4SH-H ... 

DIIOOOETHANE ACETALDEHYDE ETHYLENE OXIDE THIOACETIC-ACID ACETIC ACID METHYL FORMATE THIACYCLOPROPANE BROMOETHANE ETHYL CHLORIDE... 

Originally reported in 19 1 by Mylen and Olsen12 0 to condense with ethylene oxide to give /Miydroxyethyl thioacetate, thioaeetic acid... 

Clayfen (1.13 g, 1.2 mmol of iron(III) nitrate) is thoroughly mixed with neat thioacetal lb (0.227 g, 1 mmol) in the solid state. The material is transferred in a test tube and placed in an alumina bath inside the microwave oven and irradiated (40 s). Upon completion of the reaction, monitored on TLC (hexane-EtOAc, 8 2, v/v), the product was extracted into ethylene chloride. The resulting solution is passed through a small bed of neutral alumina. Evaporation of the solvent delivers pure p-nitrobenzaldehyde 2b in 97% yield. In the case of cyclic thio acetals and ketals, the liberated dithiols bind to the clay surface rather tightly and a simple washing of the clayfen affords clean products. 

In contrast to other methods, functional groups such as esters, amides, nitriles, alkenes, alkynes, etc. were unaffected, under these conditions. In pure methanol, ethanol or ethylene glycol, thioacetals were converted to acetals. The use of [bis(trichloroacetoxy)iodo]benzene gave equally good results [44]. Generally, since trichloroacetic acid is 3 times cheaper than trifluoroacetic acid on a mole basis, [bis(trichloroacetoxy)iodo]benzene may be an alternative to BTI. 

D-Ribopyranose tetraacetate56 has been used as a derivative for the identification of D-ribose14 and, more recently, Hardegger, Schreier and El Heweihi57 have prepared dimethyl, ethylene and dibenzyl thioacetals (mercaptals) of D-ribose for this purpose. According to Zinner58 the di-n-propyl and diisobutyl thioacetals are particularly suitable derivatives for the identification of ribose. 

Steroidal thioacetahketones. Steroidal ethylene and trimethylenc thioacetals (1) are acid-stable protective groups for ketones, but heretofore regeneration of the carbonyl function has presented dilliculties, A simple method is now available for... 

Deoxygenation of the carbonyl group of aldehydes and ketones via the intermediacy of their hydrazone derivatives, known as the Wolff-Kishner reduction,offers an alternative to the thioacetal desulfurization method. The Wolff-Kishner reduction in the presence of hydrazine and NaOH (or KOH) has been replaced largely by the Huang-Minlon method,where the deoxygenation is carried out with hydrazine in refluxing ethylene glycol. 

Treatment of the thioacetal (34) with phosphoryl chloride in pyridine gave the expected dehydration product and, with longer reaction times, the 2,3-dihydro-1,4-benzodithiin (35). Photolysis of the latter afforded ethylene and the compound (36), the stable dithiet tautomer of a dithio-o-quinone, whose structure was established by A -ray analysis. 

Ethylene and thioformaldehyde are the products of irradiation of matrix-isolated thietane at lOK. Sulphur-carbon bond homolysis has also been observed on irradiation of the nucleoside membrane transport inhibitor, 6-[ (4-nitrobenzyl) thio] -9- (/8-D-ribofuranosyl) -purine (94), and the oxazolidin-2-one (95) has been converted into the allyl derivative (96) by photochemically induced radical allylation.Efficient conversion of cyclic thioacetals into the corresponding carbonyl compounds under neutral conditions has been achieved by 2,4,6-triphenylpyrylium tetrafluoroborate-sensitised irradiation in moist dichloromethane,and diaryl sulphides and the corresponding sulphoxides and sulphones have been reported to undergo anion-promoted carbon-sulphur bond photocleavageboth processes appear to involve an initial electron transfer. Sulphur-hydrogen bond horaolysis has been reported in t-butanethiol and is also responsible for the photoinitiated thiylation of fluorobromoethylenes and of trialkylethynylsilanes and t-butylacetylene. 

Cyclic Acetals Formation of an acetal using a diol as the alcohol gives a cyclic acetal Cyclic acetals often have more favorable equilibrium constants, since there is a smaller entropy loss when two molecules (a ketone and a diol) condense than when three molecules (a ketone and two molecules of an alcohol) condense. Ethylene glycol is often used to make cyclic acetals its acetals are called ethylene acetals (or ethylene ketals). Dithiane (Section 18-8) and its alkylated derivatives are examples of cyclic thioacetals (sulfur acetals). 

Other Alkyl and Aryl Ethers.—Selective benzylation of 0-3 of methyl 4,6 O-benzylidene-a-D-mannopyranoside has been noted in the previous section, while 2,3,4,5-tetra-O-benzyl-L-arabinose diethyl dithioacetal and 2,3,4,5-tetra-O-benzyl-D-arabinose dibenzyl and ethylene dithioacetals have been prepared by benzylation of the thioacetals using benzyl chloride and potassium hydroxide. 

Further mild methods have been reported for the regeneration of carbonyl compounds from ethylene and propylene thioacetals. Conditions include reaction with methyl iodide in aqueous acetone or methanol, methyl fluorosulphonate and water in liquid sulphur dioxide, ceric ammonium nitrate in aqueous acetonitrile, and silver oxide in aqueous methanol a number of papers report the dialkylation of such acetals with methyl... 

The difficulties encountered in the regeneration of steroidal ketones from their ethylene or trimethylene thioacetals by the mercury(n) salt procedure have been circumvented 1-chlorobenzotriazole smoothly oxidizes thioacetals to the corresponding disulphoxides, which, without isolation, furnish the desired ketones in satisfactory yield on treatment with aqueous base. 

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