Dithio acetal derivative

A limited number of acyclic and cyclic prochiral dicarboxylic acid diesters were found to be good substrates for hydrolysis catalyzed by lipases (Table 11.1-12). Notable examples which give a good illustration of the potential of hydrolases as well as of the trial and error approach one relies on to a certain extent are the dithio acetal derivative 9 and the fluoro alkyl malonates 1-8. The dithio monoester 9 is obtained with different lipases with high enantioselectivities and yields despite its remote chiral center. Candida cylindracea lipase is the enzyme of choice for the synthesis of fluoro alkyl malonates with small alkyl groups. An astonishing observation was... 

A carbonyl group can be protected as a sulfur derivative—for example, a dithio acetal or ketal, 1,3-dithiane, or 1,3-dithiolane—by reaction of the carbonyl compound in the presence of an acid catalyst with a thiol or dithiol. The derivatives are in general cleaved by reaction with Hg(II) salts or oxidation acidic hydrolysis is unsatisfactory. The acyclic derivatives are formed and hydrolyzed much more readily than their cyclic counterparts. Representative examples of formation and cleavage are shown below. 

Triazoline imino sugar derivatives 297 that are prospective glycosidase inhibitors have been prepared as single diastereomers in high yield via an lAOC reaction of in situ generated azido alkene 296 (Eq. 32) [78]. m-CPBA oxidation of the dithioacetal groups in the 0-acetylated 5-azido-5-deoxydibenzyl dithio-acetal of o-xylose or D-ribose 294 to the bis-sulfone 295, followed by loss of HOAc between C-1 and C-2 provided the lAOC precursor 296. 

Dithiasuccinimides, to protect amines, 359 4H, 7//-1,3-Dithiepin derivatives, to protect carbonyl groups, 207 Dithio acetals and ketals to protect carbonyl groups, 7, 157,... 

Carbonyl functions often are protected as thioacetals, because these derivatives are stable to acids and bases. Dithio-acetals and -ketals generally are prepared by reaction of the carbonyl compound with a thiol in the presence of an acid catalyst. This transformation has been used in carbohydrate chemistry for a long time to lock aldoses in their acyclic forms (see equation 26). In recent years, this blocking principle for carbohydrates has been exploited in several chiral pool syntheses. Several other methods for... 

Acylation66 of D-fructose leads67 to substantial yields of a completely esterified, acyclic derivative (6) in which the ketonic center exists as a free carbonyl group, and provides an indirect route for the synthesis of ketose dialkyl dithioacetals, as 6 reacts with two equivalents of thiol under acid catalysis to produce68 the acylated dithio-acetal 7, which can subsequently be saponified to yield the free... 

Recently, the one-pot four-component synthesis of rhodanine derivatives was also reported. In this chapter, a novel multicomponent synthesis of ketene dithio-acetal rhodanines was reported by the reaction of primaiy amine, carbon disulfide, ethyl chloroacetate, and alkyl halide in dimethylfonnamide (DMF Scheme 9.10). When 1,2-dibromoethane 12 is used as an alkyl halide, 1,3-dithiolane is formed at the 5-position and linked by a double bond. According to the literature, potassium carbonate was the best candidate for catalyzing the reaction in moderate-to-good yields at room temperature [22]. 

Diseleno acetals and ketals are cleaved more rapidly than their dithio counterparts a methyl derivative is cleaved more rapidly than a phenyl derivative. Methyl iodide or ozone converts diseleno acetals and ketals to vinyl selenides. ... 

Thiophenyl acetates (366 R = Me) and propionates (366 R = Et) react with electrogenerated polysulflde ions S3 in DMF to yield thiocarboxylate ions, thiolate ions, and phenyl tetrasulfanide (367), the last deriving from the reaction of thiolate ions with sulfur (Scheme 48). Smdies of the aminolysis by a set of substimted anilines of Y-aryl dithio-2-thiophenates (368 X = S) and dithio-2-furoates (368 X = O) in acetonitrile have shown that the rate-determining step in these reactions is the departure of the thiophenolate ion from the zwitterionic tetrahedral intermediate T= = (Scheme 49). Experiments with deuteriated anilines yielded k i/IcQ values of 1.7-1.9,... 

Like the corresponding 1,2-dithiole derivatives (Section II,B,7,d)> 2-phenacylthio-l,3-dithio]ium ions 190, treated by triethylamine in acetic acid undergo an internal rearrangement, yielding first the disulfide 191 and then 192. ... 

Substituted 5-Methyl Derivatives Monothio, Dithio, and Aminothio Acetals 669... 

Lithium-halogen exchange. The reagent is useful for preparation of organo-lithiums from acetal-containing substrates, dihaloarenes (monofunctionalization), and halopyridines. Dechlorination of /V-(/3-chloroalkyl)amides apparently cannot be achieved with BuLi alone (stops at (V-deprotonation ), and the use of LN is required." Of course the N,C-dithio derivatives may be employed in C-C bond formation (remarkably the coupling with aryl and vinyl halides). Barbier-type reactions have been achieved."... 

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