Variations
When using oxalyl chloride as the dehydration agent, the reaction must be kept colder than −60 °C to avoid side reactions. With cyanuric chloride or trifluoroacetic anhydride instead of oxalyl chloride, the reaction can be warmed to −30 °C without side reactions. Other methods for the activation of DMSO to initiate the formation of the key intermediate 6 are the use of carbodiimides (Pfitzner–Moffatt oxidation) and pyridine-sulfur trioxide complex (Parikh-Doering oxidation). The intermediate 4 can also be prepared from dimethyl sulfide and N-chlorosuccinimide (the Corey-Kim oxidation).
In some cases, the use of triethylamine as the base can lead to epimerisation at the carbon alpha to the newly formed carbonyl. Using the bulkier base diisopropylethylamine (iPr2NEt, Hünig's base) can mitigate this side reaction.
Read more about this topic: Swern Oxidation
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