1.2- Dithianes

The carbanions derived from thioacetals, however, are typical -synthons. Most frequently used are 1,3-dithianes and C -silylated thioethers (see p. 33f. D. Seebach, 1969, 1973 B.-T. Grobel, 1974,1977). In these derivatives the proton is removed by butyllithium in THF. 

Dithiane, 2-phenyl-bond angles, 3, 949 conformation, 3, 949 structure, 3, 949 sulfoxide... 

Methylthiomethyl ethers are quite stable to acidic conditions. Most ethers and 1,3-dithianes are stable to the neutral mercuric chloride used to remove the MTM group. One problem with the MTM group is that it is sometimes difficult to introduce. 

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. 

RSSiMe3 [R = Me, Et, (-CH2-)3], Zn, Et20, 0-25°, 70-95% yield. This method is satisfactory for a variety of aldehydes and ketones and is also suitable for the preparation of 1,3-dithianes. Methacrolein gives the product of Michael addition rather than the thioacetal. The less hindered of two ketones is readily protected using this methodology. ... 

A 1,3-dithiane is stable to the conditions (HgCl2, CaC03, CH3CN-H2O, 25°, 1-2 h) used to cleave a methylthiomethyl (MTM) ether (i.e., a mono-thio acetal). ... 

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