Monothioacetals, conversion

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>. 

The different reactivities of the two substituents on C-l allow selective replacement and conversion of them. Alkyl monothio-acetals [proposed as intermediates in mercury(II)-catalyzed demer-captalation reactions—see Section IV,l,b] have been prepared from a-bromothioethers by the combined action of an alcohol and silver(I) carbonate the introduction of S-nucleophiles is discussed in Section 11,6. Reduction of 81 by lithium aluminum hydride effects hydrogen-olysis of the carbon-halogen bond, whereas the action of Raney nickel on the derived S-ethyl O-methyl monothioacetal specifically cleaves the carbon-sulfur bond to afford the pentaacetate of 1-0-methyl-D-galactitol.327... 

Conversion of aldopyranosides into 5-thioaldopyranosides via acyclic monothioacetals was proposed by Hashimoto et The method involves the... 

A deboronation method which converts organoboranes directly into protected aldehydes under mild, basic conditions has been reported, in which a-(phenyl-thio)alkylboranes are selectively cleaved by N-chlorosuccinimide in basic methanol to yield monothioacetals or, with excess reagent, dimethyl acetals. The conversion of aldehydes and ketones into selenoacetals via the crystalline reagent tris(phenylseleno)borane has also been published. ... 

A procedure for reductive sulphidation, i.e. the conversion of a carbonyl compound into a sulphide, involving the formation and reduction of o-trimethylsilyl monothioacetals has been reported (Scheme 28). ... 

---