Dithioacetals conversion

Another indirect method is conversion of the aldehyde or ketone to a dithioacetal or ketal, and desulfurization of this (14-34). 

The conventional conversion of carbonyl systems by sulphur tetrafluoride into difluoroalkyl compounds has been modified in the reaction of dithioacetals with tetra-n-butylammonium dihydrogentrifluoride and A -bromo- or AModosuccinimide. Yields of the difluoroalkanes are generally in excess of 70% [35]. 

Cyanogen Iodide (ICN) has been used extensively for the cyanation of alkenes and aromatic compounds [12], iodination of aromatic compounds [13], formation of disulfide bonds in peptides [14], conversion of dithioacetals to cyanothioacetals [15], formation of trans-olefins from dialkylvinylboranes [16], lactonization of alkene esters [17], formation of guanidines [18], lactamization [19], formation of a-thioethter nitriles [20], iodocyanation of alkenes [21], conversion of alkynes to alkyl-iodo alkenes [22], cyanation/iodination of P-diketones [23], and formation of alkynyl iodides [24]. The products obtained from the reaction of ICN with MFA in refluxing chloroform were rrans-16-iodo-17-cyanomarcfortine A (14)... 

Acetals are usually easy to cleave by acid-catalyzed transacetalization or hydrolysis (Table 3.40). Dithioacetals, on the other hand, tend to be more resistant to hydrolysis, but cleavage can be achieved by treatment with mercury(II) salts or by oxidation with either [bis(trifluoroacetoxy)iodo]benzene [723] or periodic acid [724]. Use of the latter reagent can, however, also lead to the conversion of methyl ketones into iodo-methyl ketones [721],... 

When using dithioacetals as intermediates the most tedious step is often their hydrolysis to carbonyl compounds. As a consequence, many methods have been developed to realize that conversion and, in their review [43], Grobel and Seebach give experimental details for most of the procedures known at that time. In view of the fundamental importance of dethioacetalization, we now describe some promising new methods that have appeared since. 

The possibility of conversion of the dithioacctal into the corresponding ketone without reconjugation of the double bond is a noteworthy j feature of this synthetic scheme. The syntheses of iso-ar-turmerone and isoartemisia ketone mentioned above proceeded similarly via a carbophilic pathway. In the latter case a p-ethylenic dithioester was not isomerized during the following overall sequence carbophilic addition-methylation-dithioacetalization [343]. ... 

The conversion of dithioesters into aldehydes is also easily realized through reduction to a mixed dithioacetal by tributyltin hydride [264]. 

J. Defaye and D. Horton, Correlation of conformational stability of pentose dialkyl dithioacetals and their conversion into 2,5-anhydro derivatives upon attempted /)-tolucncsuIIbnylation, Carbohydr. Res., 14 (1970) 128-132. 

The cyclodehydration of 18 to the anhydroalditol derivative 19 has been explained as an attack by the 6-hydroxyl group on the double bond. Studies by Hall et al.59 of acyclic sulfones formed from two heptose dithioacetals epimeric at C-2 revealed their ready conversion in hot water into a common... 

Fig (19) Octalin ketal (163) is converted to kete dithioacetal (164) by the cleavage of ketal function and condensation with carbon disulfide and methyl iodide. Subjection of (164) to the action of dimethylsulfonium niethylide and acid hydrolysis leads to the formation of unsaturated lactone (165).lts furan silyl ether derivative is caused to undergo Diets-Atder reaction with methyl acrylate to obtain salicyctic ester (166) which is converted by standard organic reactions toabietane ether (167). It is converted to aiiylic alcohol (168) by epoxidation and elimination. Alcohol (169) obtained from (168) yields orthoamide which undergoes transformation to amide (170). Its conversion to the previously reported intermediate has been achieved by epoxidation, elimination and hydrolysis. 

It has been demonstrated that reactions of ketene dithioacetals with suitable glycine derivatives provides convenient access to a variety of densely substituted pyrroles, as illustrated for instance by conversion of the readily available substrate 412 into the product 413 (Equation 117) <2005SC693>. 

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