Stereoselective Synthesis of Asymmetric Sulfoxides

It has been shown66 that, whereas oxidation of 104 with sodium periodate affords a mixture of the axial and equatorial sulfoxides, 102 and 103, in which the equatorial sulfoxide preponderates (the ratio of 102 103 is 10 1), similar oxidation of 105 affords a mixture of 106 and 107 in which the axial isomer preponderates (ratio of 106 107, 

On the basis of these and related results, and because variation of the oxidant did not produce the clear-cut differences in the steric course of oxidation observed with thianes, it was suggested66 that control of the S-oxidation of derivatives of 2-hydroxy-l,4-oxathiane is best achieved by changing the configuration at the anomeric center an axially attached substituent such as methoxyl or acetoxyl engenders equatorial S-oxygenation, whereas an equatorially attached, anomeric substituent leads to an axial S-oxide. 

The ease of reduction of sulfoxides with diborane also depends on the configuration of the sulfoxide.64 Thus, in such compounds as 106 and 107, reduction of the equatorial sulfoxide is favored, presumably because diborane attacks the less-hindered sulfoxide oxygen atom. However, with the sulfoxide pair 102 and 103, the axial sulfoxide is reduced to a greater extent than the equatorial one. The role of the axially attached substituents on C-2 in promoting reduction of the axial sulfoxides is not yet clear. From such studies, the mechanisms of oxidation of sulfides to sulfoxides, and the reduction of sulfoxides to sulfides, will, perhaps, become sufficiently well elucidated to be of value in establishing the configuration of sulfoxides. 

Department of Chemistry, The Rostov State University, Rostov-on-Don, U. S. S. R. 

Types of Final Products and Their Utilization in Synthesis.232 

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