Menthol tosylates

Sulfonate esters are also reduced to hydrocarbon with LiAlH4 via cleavage of the C-O bond. For example, menthol tosylate (6.82) gave the menthane (6.83) in 60% yield. 

In addition to sulfimides, the nitrogen analogs of sulfinates and sulfinamides are chiral and have been obtained as optically active compounds. For instance, the synthesis of diastereomeric menthyl p-toluenesulfinimidoates 90 mentioned above was effected by Cram and his collaborators (18,137) on two ways. The first comprised the reaction of racemic A -tosyl-p-tolueneiminosulfinyl chloride 92 with menthol, followed by separation of the diastereomers of 90, whereas in the second method the reaction of the ester (->45 with chloramine T was utilized. 

The analogues [menthyloxy(tosyloxy)iodo]benzenes, with both (+) and (-) forms of menthol, in their reactions with non-symmetric sulphides caused considerable asymmetric induction hydrolysis of their salts afforded sulphoxides of high optical purity [52]. By using A-phenyliodonio tosylates of benzamide (and some other similar derivatives from different amides, Section 7.4.1) dimethyl sulphide was converted into amidosulphonium tosylates which can serve as the precursors of sulphilimines [51] ... 

Menthol and neomenthol have the structures I and II, respectively, and differ only in the configuration of the hydroxyl. When they are converted to their tosylates and the latter are treated with sodium ethoxide in ethanol, the following reactions occur predominantly. 

Since we are told that menthol gives rise ro structure I, its tosylate must have structure A. Menthol must therefore have an equatorial hydroxyl. By the same principle neomenthol must have an axial hydroxyl. 

Since the tosylate of menthol must be in a boat conformation in order for anti-elimination to occur, its rate of product formation must be slower than that of neo-menthol. This is due to the fact that the boat conformation is at an energy maximum, approximately 7-1 kcal/mole less stable than the chair conformation. Because the boat conformation is at an energy maximum, it is really not a conformer at all instead, it can be considered as a transition state between two conformers. As such, its probability of existence at a given time is very low, and it probably occurs at a ratio of 1 to 10,000 when compared to the more stable chair conformation at room temperature. 

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