Sulfide, diisopropyl oxidation

Diethyl tartrate is the best tartaric acid derivative for enantioselective oxidation of thioethers. This finding was established for the asymmetric oxidation of methyl p-tolyl sulfide with cumene hydroperoxide, that is, 96% ee (DET) 87% ee (diisopropyl tartrate) 62% ee (dimethyl tartrate) [24] and 1.5% ee (bis A, V-dimethy I tart rami de, r-BuOOH as the oxidant) [17]. 

Interestingly, it is possible to employ diisopropyl sulfide in the place of dimethyl sulfide in Corey-Kim oxidations, in which case primary alcohols can be oxidized in the presence of secondary ones or vice versa, depending on reaction temperature.250... 

Interestingly, when a Corey-Kim oxidation (Me2S/NCS) is performed with diisopropyl sulfide, instead of dimethyl sulfide, primary alcohols are selectively oxidized at 0°C, while lowering the temperature to —78°C causes the selective oxidation of secondary alcohols.34... 

A classical Corey-Kim oxidation sometimes shows a certain preference for the oxidation of secondary alcohols.2 Additionally, a Corey-Kim oxidation, in which diisopropyl sulfide is employed in the place of dimethyl sulfide, presents a preference for the oxidation of primary alcohols at 0°C and secondary alcohols at -78°C.50... 

With some oxidants, interesting regioselectivity was obtained by varying the temperature conditions. Whereas the diisopropyl sulfide-Wchlorosuc-cinimide preferentially oxidizes primary hydroxyl groups at 0°C, at —78°C secondary groups are oxidized selectively (Scheme 25).439b... 

Oxidation of primary and secondary alcohols. In contrast to dimethyl sulfide-NCS (4, 88-90), which oxidizes both primary and secondary alcohols, diisopropyl sulfide-NCS can effect selective oxidation of these substrates. At 0° it oxidizes only primary alcohols to aldehydes, but at —78° it oxidizes only secondary alcohols to ketones. However, allylic or benzylic alcohols are oxidized at either temperature. 

The use of A(-chlorosuccinimide/diisopropyl sulfide for the selective oxidation of primary/secondary diols was outlined earlier in Section 2.9.2.1, where it was used for the selective oxidation of the primary alcohol. Remarkably, by carrying out the reaction at -78 C (as compared to O C in the previous case) this reagent system becomes selective for secondary alcohols in the presence of primary alcohols (see Scheme 2 Section 2.9.2.1). 

An interesting example of this type of chemoselective oxidation has been reported with die reagent mixture derived from diisopropyl sulfide and iV-chlorosuccinimide. This reagent will oxidize selective ly a primary alcohol to an aldehyde at 0 C. Surprisingly, this same reagent at -78 C will oxidize selec lively a secondary alcohol to the corresponding ketone (Scheme 2). Allylic and benzylic alcohols are oxidized at both temperatures. 

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