Monothioacetic acid

C12 2oOsRh2S6f Tetra M monothioacetatO bis(monothioacetic acid rhodium), 43B, 1233... 

By reaction of 5-chloro-2,3,6-trifluoropyridine (171) with vinylstannane 172 and monothioacetic acids (173) 5,6-difluoro-2,3-dihydrothieno[2,3-b]pyridine (174) was obtained and used as precursor for synthesis of anticancer drugs [118] (Scheme 56). 

T AHBr, AcOH, rapid. The 5-isobutoxymethyl monothioacetal is stable lo 2 N hydrochloric acid and to 50% acetic acid some decomposition occurs m2 N sodium hydroxide. ... 

The monothioacetal is also stable to 12 N hydrochloric acid in acetone (used to remove an TV-triphenylmethyl group) and to hydrazine hydrate in refluxing ethanol (used to cleave an A -phthaloyl group). It is cleaved by boron trifluoride etherate in acetic acid, silver nitrate in ethanol, and tiifluoroacetic acid. The monothioacetal is oxidized to a disulfide by thiocyanogen, (SCN)2- ... 

Examples of nucleophilic attack at the saturated 2-carbon of dihydro-l,4-thiazines, which may be assisted by the neighboring sulfur atom, are shown below. The nucleophiles include water, which was used in the acid-catalyzed hydrolysis of the ketal in 236 (Equation 21) <1982S424>, methanol in the conversion of 214 into a monothioacetal (Equation 22) <1982JHC131>, ethanol and dimethylaniline, which both reacted with 237 (Scheme 29) <1982TL4963>, and triethyl phosphite that was used to convert 238 into the phosphonate 239 required for Wadsworth-Emmons reaction (Equation 23) <2004BML1477>. Compound 240 reacted with both methanol and methanethiol (Equation 24) <1990JME1898>. 

Explain why compound 2 hydrolyzes at a rate that is independent of pH in the range pH 1.5 to 0.1 M NaOH, despite the fact that as a general rule acetals and monothioacetals show strong acid catalysis. 

The hemiacetal thiol 75 (Fig. 13) gave on acid cyclization an equilibrium mixture of cis and trans monothioacetals 76 and 77 in a 1 1 ratio (63). If a value of 1.7 kcal/mol is accepted for the steric effects in 76 (two gauche forms of SCl XCHg = 0.8 kcal/mol and one gauche form of butane= 0.9 kcal/mol), the anomeric effect for the ether oxygen in 76 must also be equal to 1.7. 

Eliel and Giza (50) have studied the acid equilibration of the isomeric 2-alkylthio 6-methyltetrahydropyrans 59 and 60 (R=CHj and (CH3I3C). They found about 65% of axial isomer 59 indicating that the monothioacetal function possesses an anomeric effect although it is weaker than that of the acetal function. Zefirov and Skekhtman (58) have arrived at a similar conclusion by studying 2-phenylthio and 2-ethylthiotetrahydropyran. 

The reaction of HFA with hydrogen sulfide 136) and mercaptans 103, 150) yields hemimercaptals 126 at moderate temperatures in analogy to Eqs. (79), (81), and (84)-(87). Monothioacetic 206), trifluoroacetic 218), and benzoic 206) acids react similarly. 

Molecular sieves, 55, 130, 316-317 Molybdenum carbonyl, 317 Monensin, 136, 137, 173 Monoisopinocampheylboranc, 317 Monothioacetals, 6-7 Monotrimethylsilyl acetamide, 113 Morpholine, 138, 139 Morpholine-Camphoric acid, 317-318 Morpholine enamines, 319 N-Morpholinomethyldiphenylphosphine... 

Benzenethiol (9) itself can partake in 1,4-addition to the methyl ester 10 of 2-fluoro-3-methoxy-acrylic acid to yield the monothioacetal ll.40... 

Antimony-sulphur compounds are quite widespread and stable, probably a consequence of soft acid-soft base interaction, and the solid state structures are characterized by the formation of a number of weaker Sb... S secondary bonds. In phenylantimony bis(monothioacetate), the ligands are bonded primarily via sulphur (Sb—S 2.451, 2.471 A), but, as Sb(III) is coordinatively unsaturated, there is substantial secondary interaction with the oxygen atom of the thioacetate (mean Sb...02.81 A) giving a bis chelate structure with antimony in distorted square-pyramidal coordination . The apical position is occupied by the phenyl group and the two sulphur atoms are eis to each other (S—Sb—S 84.8°) in the basal plane. Weak dimers are present in the solid state as a result of Sb... S bonding to the sulphur forming the longer Sb—S bond. 

Nishiyama, H., Narimatsu, S., Sakuta, K., Itoh, K. Reaction of allylsilanes and monothioacetals in the presence of Lewis acids regioselectivity in the cleavage of the acetals. J. Chem. Soc., Chem. Commun. 1982,459-460. 

The 5-isobutoxymethyl monothioacetal is cleaved by boron trifluoride etherate in acetic acid, by silver nitrate in ethanol, and by trifluoroace-tic acid. The monothioacetal is oxidized to a disulfide by thiocyanogen,... 

Alkoxytetrahydrothiopyrans were studied by Zefirov and Shekhtman [35] and the axial conformer 233 was found to predominate (90 %) over the equatorial con-former 234 when R was a methyl or a propyl group. The equilibrium of the isomeric mixture of 235 and 236 under acidic conditions was studied by Eliel and Giza [36]. The axial isomer 235 was found to constitute almost 65 % of the mixture. These examples indicate that a monothioacetal function benefits from anomeric effect arising from sulfur, which is possibly a bit weaker than that offered by oxygen. 

Allylsilanes react with alkoxymethyl and phenylthiomethyl chlorides in the presence of Lewis acids (Scheme 53), and dithioacetals, similarly, where substantial stereoselection can be achieved with large aryl groups on the sulfur atoms (Scheme 54). Monothioacetals react selectively with cleavage of the carbon-sulfur bond when tin(IV) chloride is used as the Lewis acid (Scheme 55). ° ... 

Allylstannanes are much better nucleophiles for dithioacetals than allylsilanes, and dimethyl(methyl-thio)sulfonium fluoroborate is a particularly good catalyst in this reaction. The reaction has been used tellingly in a macrocyclization (Scheme 56). ° Monothioacetals also react with allylstannanes, with cleavage of either the carbon-oxygen or the carbon-sulfur bond, depending upon the choice of Lewis acid (Scheme 57).Sugar thioacetals react in the same way (Scheme 58), but with the opposite anomeric stereoselectivity from that of the corresponding radical chain substitution. ... 

Formation of spiro orthoesters such as 4 is achieved in high yield by reaction of cyclic ketene monothioacetals such as 3 with ethanediol and camphorsulfonic acid <04SL2013>. A variety of substituted epoxy ketones 5 rearrange to the benzodioxoles 6 upon treatment with Bu.,N CN in CHjClj or K1 in acetone <04T3825>. Condensation of phenacyl carbonates 7 with aromatic aldehydes in the presence of MgCClO ), 2,2 -bipyridyl, A-methylmorpholine and molecular sieves gives the trans dioxolanones 8 <04SL1195>. 

Monothioacetals 1,3-Oxathiolanes Thioesters. See Carbothioic or Sulfonothioic acids, 5-esters... 

The facility with which the phosphorus-carbon bond in acylphosphonic derivatives is cleaved by the action of the more basic nucleophiles has already been commented upon. Those nucleophiles include alkoxides and amines, but it may be noted that thiols undergo normal addition to the carbonyl group. With regard to the latter, diethyl acetylphosphonate yields the monothioacetals 256 the derivatives may not be stable thermally but their decomposition occurs with cleavage of the phosphorus-carbon bond Reactions between the same substrate and simple carboxamides in the presence of an acid catalyst under dry conditions furnish the acylated enamides 257 ". ... 

Hydroxythioethers Monothioacetals Monothioketals Sulfines Thiolactones ThioUc acid esters... 

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