Indolic Swern oxidation

The oxidation of the primary alcohol leads to an aldehyde that is isolated as an aminal. Minor amounts of a methylthiomethyl ether are isolated, resulting from the reaction of the alcohol with CH2=S(+)-Me that is formed by thermal decomposition of activated DMSO. Interestingly, a Swern oxidation fails to deliver the desire product, because it causes the chlorination of the indole. 

While the Parikh-Doering oxidation succeeds, a Swern oxidation produces chlorination at the activated 3-position of the indole. ... 

Swern oxidation of various indolic substrates has been described, and a range of products resulting from overall oxidation at the 2-position have been observed. For example, indolylpropanol 1809 [R = (CH2)30Hj is oxidized with DMSO and either trifluoroacelic anhydride or oxalyl chloride to give the unsaturated aldehyde 1810 [R = (CH2)2CH0] [1333]. 

Oxidation of amines to imines.1 This Swern reagent effects oxidation of ben-zylamines to the corresponding Schiff bases in 40-60% yield. It also oxidizes in-doline to indole in 88% yield. 

Depending on the substrate and the reaction conditions, indolealkyl alcohols may be oxidized to a,yS-unsaturated systems, and indoles can either be oxidized to introduce a nucleophile regioselectively at the 2-position or to introduce both a nucleophile at the indole 2-position and a MeSCH2 group at the indole 4-position through an unprecedented rearrangement of a Swern intermediate [1333]. 

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