Di thioacetals

Schlessinger has shown that the addition of ester enolates to sulfur stabilized acceptors, e.g. ketene di-thioacetal monoxide (151) and methyl a-(methylthio)acrylate (187), is highly efficient for the synthesis of Y-ketoesters.148 Similarly, Ahlbrecht and Seebach have reported that amide and ester enolate additions to nitrogen stabilized acceptors, e.g. nitroalkenes (40) and 2-(/V-methylanilino)acrylonitrile (59 Scheme 72), are highly efficient.149... 

S4 (di-thioacetal) (1,3,7,9) 12UT-1 2-Octyl-12S4 4,6-Dithianonane-l,9-dithiol + methylene bromide t -l, 2-l)ichloroethylcnc + Na2S 4-Octyl-3,6-dithiaoctane-l,8-dithiol + 1,1-dibromoethane... 

This species can react with a sugar alcohol to form a disaccharide. The ready availability and stability of 75 and this selective and mild glycosylation procedure render this method synthetically attractive. Anodic oxidation of diaryl di-thioacetals results in S-S bond formation as well as C-S bond cleavage as shown inEq. (33) [176,177] ... 

This reaction provides a synthesis of r/oos-calamene (7) from the ketene di-thioacetal (5) of /-menthonc. 

S. Honda, Y. Takai, and K. Kakei, Periodate oxidation analysis of carbohydrates. Part 12. Rapid determination of aldehydes in the oxidation products of oligoglycosides by the di-thioacetal method, Anal Chim. Acta, 105 (1979) 153-161. 

Tri-O-benzyl-D-arabinofuranose stirred at 0° with a mixture of ethanethiol and anhydrous Mg-sulfate satd. with HGl, and the product treated with benzoyl chloride in pyridine 4-0-benzoyl-2,3,5-tri-0-benzyl-D-arabinose diethyl di-thioacetal (Y 94%) added with Drierite to henzyl alcohol, stirred 1 hr. after addition of Cd-carbonate and HgClg the product isolated after 2 hrs. -> 4-0-benzoyl-2,3,5-tri-0-henzyl-D-arabinose dibenzyl acetal (Y 80%) stirred 16 hrs. under reflux at 56-58° with BaO, Drierite, methyl iodide, and dimethylformamide, the resulting crude 2,3,5-tri-0-henzyl-4-0-methyl-D-arabinose dibenzyl acetal hydrogenated ca. 2.5 hrs. with palladous chloride in methanol, and the product refluxed 1.5 hrs. in 0.5 N HGl to hydrolyze the methyl glycoside present 4-0-methyl-y -D-arabinopyranose (Y 64%). — This pathway is not dependent on the stereochemistry of the aldose. H. G. Fletcher, Jr., and H. W. Diehl, J. Org. Ghem. 30, 2321 (1965). 

Lr. and Raman spectra of aryl mono- and di-thioacetals have been studied in comparison with those of analogous sulphides, showing some characteristic band patterns in the 1000—1650 cm region. 

Lewis acid, and the temperature were optimized to control the degree of degradation and to prevent the formation of undesired di-thioacetal cleavage products. 

Although detailed mechanistic studies of the metal cleavage of mono- or di-thioacetals have not appeared the general pathway is probably analogous to the metal-catalyzed cleavage... 

A new di-O-benzylidene derivative (13) of D-arabinose diethyl di-thioacetal was obtained by benzylidenation with -dimethoxytoluene,... 

When 2-4-0-ethylidene-D-glucofuranurono-6,3-lactone [obtained by the hydrolysis of thioacetal 61 (Ph = Et)] was treated with 5,5-dimethyl-l,3-cyclohexanedione (dimedone), 6-deoxy-6,6-bis(4,4-di-methyl-2,6-dioxocyclohexyl)-3,5-0-ethylidene-L-gulono-1,4-lactone (73) was formed in 71% yield.99... 

In another approaeh [88IJC(B)570], reaetion of 2-mereapto-4,5-di-p-tol-ylimidazole 43 with a-halo carboxylie acids enabled the synthesis of several imidazo[2,l-h]thiazoles. Acylative ring closure of 4,5-di-p-tolylimidazo-2-thioacetic acid (44, R = H) or 2-thiopropionic acid (44, R = Me) provides 5,6-di-p-tolylimidazo[2,l-h]thiazole-3(2//)-one (45, R = H) or its 2-methyl analog (45, R = Me). The synthesis of annelated imidazo[2,l-h]thiazoles (e.g., 46) can be achieved in one step by reaction of 2,3-dichloroquinoxaline with 43. The intramolecular eyelization of l-vinylimidazole-2-thiones to 2,5-dimethyl-3,6-arylimidazo[2,l-h]thiazoles with excellent yield has been reported (93T6619). 

The three l,4 3,6-dianhydrohexitols show the shielding effect of the cts-fused oxolane ring on their di-O-sulfonyl derivatives. As C-2 and C-5 of 1,4 3,6-dianhydro-D-mannitol 2,5-di-p-toluene-sulfonate and 2,5-dimethanesulfonate are open to attack from the exo direction, they react readily with such nucleophilic reagents as benzoate in /V,iV-dimethylfoimainide,94 acetate in acetone,93 thioacetate,95 phthalimide in A/,JV-dimethylformamide,93 and iodide in acetic anhy-dride.59<6) Inversion occurs at these positions and the L-iditol configuration results, as pointed out in the several examples in Table V. However, hydroxide ion may merely saponify,92 with retention of configuration.93... 

Ketcnc equivalents, such as ketene acetals and thioacetals, can be used in cycloadditions to electron-deficient alkenes (see Sections 1.3.2.1. and 1.3.2.2.). In an example of a fumaric acid diester fitted with two chiral alcohol auxiliary groups, the aluminum(III)-catalyzed cycloaddition of 1,1-dimethoxyethene with di-(—)-menthyl fumarate (9) proceeds with > 99% diastereomeric excess. Intermediate 10 can be readily converted to cyclobutanone derivatives.17, 18... 

Several cyanodithioformates are mentioned in ref. 1. The coordination chemistry of monothio-carboxylates deals almost exclusively with thioacetates and thiobenzoates. Structures of several monothiobenzoates are based on IR data.42 Those, however, of the copper(I) and silver(I) complexes are doubtful. They are probably polymeric and of the same structural class as the mono- and di-thiocarbamates43-45... 

Borate complexes have been utilized by Brigl and Griiner47 to effect partial esterification. Anhydrous D-glucose and metaboric acid dissolved in acetone give a complex which exhibits the analysis of a diborate. Reaction of the latter with an excess of benzoyl chloride gives 2,6-di-O-benzoyl-D-glucose (XL). D-Mannitol likewise forms a diborate, which produces the 1,6-di-O-benzoyl derivative (XLI) upon benzoylation. In the presence of boric acid, D-glucose diethyl thioacetal yields the 6-benzoate (XLII). In the non-aqueous medium the formation of complexes... 

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