Thioacetals, oxidative cleavage

An interesting application of the cydization of alkenyl thioacetals is the stereoselective preparation of olefmic diols. Thus, oxidative cleavage of the silicon—carbon bond [32] in the ring-closed metathesis products, i.e. cyclic allylsilanes such as 35 and 36, affords (Z)-alk-2-ene-1,5-diols 37 and 38 (Scheme 14.18) [33],... 

Potassium nitrosodisulfonate, 258 Trimethylsilyl chlorochromate, 327 By hydrolysis of acetals or thioacetals Amberlyst ion-exchange resin, 152 Methylthiomethyl p-tolyl sulfone, 192 By isomerization of allylic alcohols N-Lithioethylenediamine, 157 By oxidation of aromatic side chains Trimethylsilyl chlorochromate, 327 From oxidative cleavage of alkenes [Bis(salicylidene-7-iminopropyl)-methylamine]cobalt(II)... 

Stable nitronium (N02+) salts, particularly with PFfi and Bl, counterions, can act as mild, selective oxidative cleavage reagents for a wide variety of functional groups.497 99 Examples such as the oxidation of methyl ethers [Eq. (5.187)], oximes [Eq. (5.188)], dimethylhydrazones [Eq. (5.189)], and thioacetals [Eq. (5.190)] illustrate the utility of these methods. 

Oxidative cleavage of the C-S bond takes place while treating steroid thioacetals 135 with CBT. As a result ketones 136 are formed [71JCS(CC)750] (Scheme 130). 

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] ... 

Cleavage of tUoaceta groups. Sulfuryl chloride in the presence of wet silica gel oxidatively cleaves thioacetal groups at room temperature. Monosulfoxides arc presumably intermediates. ... 

Regeneration of carbonyl compounds from 1,3-dithian 1-oxides can be accomplished using triethyloxonium tetrafluoroborate. Nitrosonium salts, and nitronium salts, either preformed or prepared in situ, are effective reagents for the cleavage of dithioacetals. Similarly hydrolysis of thioacetals can be performed with thallium trinitrate, and selective hydrolysis can also be achieved with this reagent [equation (59)]. ... 

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