Sulphur stereochemistry

Chiral sulphoxides are the most important group of compounds among a vast number of various types of chiral organosulphur compounds. In the first period of the development of sulphur stereochemistry, optically active sulphoxides were mainly used as model compounds in stereochemical studies2 5 6. At present, chiral sulphoxides play an important role in asymmetric synthesis, especially in an asymmetric C—C bond formation257. Therefore, much effort has been devoted to elaboration of convenient methods for their synthesis. Until now, optically active sulphoxides have been obtained in the following ways optical resolution, asymmetric synthesis, kinetic resolution and stereospecific synthesis. These methods are briefly discussed below. 

It is significant to note that the above /J phenylthiophene should offer greater stability toward racemization than the a-phenylthiophene previously studied in our laboratory (64) due to the presence of four o-substituted groups as well as to the fact that the sulphur atom is further removed from the pivot bond. Hence, it should lend itself more readily to optical studies and so open a new field of exploration within the scope of this type of stereochemistry. 

The reaction, which is accelerated by catalytic amounts of sulphuric acid, exhibits a predominantly iyn-stereochemistry. 

The stereochemistry of hydration of fumaric acid in (1) sulphuric acid catalyzed hydration and in (2) enzyme catalyzed hydration from the following information—... 

The structure of ds-bis-(iV-isopropyldithiocarbamato)nickel(ii) is the first example of cis configuration in complexes of this kind, all previously reported examples have had a trans structure. The adoption of a cis stereochemistry is due to the strong hydrogen bonding between the HN1 hydrogen and sulphur atoms in neighbouring molecules.530... 

Whereas oxygen nucleophiles gave poor yields of alkenylated products with alkenyl iodonium salts, the reactions with sulphur nucleophiles proceeded more efficiently, leading to unsaturated sulphides and sulphones. Thus, 4-t-butylcyclohexenyl phenyliodonium salts afforded with sodium thiophenoxide 4-t-butylcyclohexenyl phenyl sulphide (81%) [3] and with sodium phenylsulphinate the corresponding sulphone (29%) in the presence of 18-crown-6, the yield of the latter rose to 80% [45]. jS-Phenylsulphonylalkenyl iodonium salts with sodium phenylsulphinate at 0°C, without any catalyst, afforded Z-l,2-bis(phenylsulphonyl)alkenes, in high yield with retention of the stereochemistry [45] ... 

In a similar process to halofluorination, sulphur- [285], selenium- [286] and nitrogen-containing [43] groups and fluorine may be added to hydrocarbon double bonds by reaction of an alkene with an electrophilic reagent of the heteroatom species in conjunction with a fluoride-ion source (Figure 3.66). As expected, Markovnikov addition in trans stereochemistry occurs mainly. 

A c.d. correlation confirmed that (+ )-5-carotene (20) has the same absolute stereochemistry at C-6 as (-f )-a-carotene (21). Lutein (22) was also shown to have this absolute stereochemistry at C-6 by c.d. correlation with natural zein-oxanthin (23). In order to do this, the allylic alcohol group was removed by Corey s method using the sulphur trioxide-pyridine complex followed by... 

After some introductory remarks on the stereochemistry of oxygen and some of the differences between oxygen and sulphur we deal with simple molecules and ions containing oxygen and then with the following topics ... 

Since the stereochemistry of a molecule S 2R2 is similar to that of a sulphur chain S the following remarks apply equally to three main groups of compounds molecules S 2R2, polysulphide ions S , polythionate ions S Og and closely related molecules such as TeS i04R2. 

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