DDQ reactions

In comparison with manganese dioxide, the DDQ reagent has several advantages for the oxidation of allylic alcohols. The quinone method is more reproducible only one equivalent of oxidant need be added and generally fewer side reactions are observed. On the other hand, the workup of DDQ reactions often requires chromatography and in the simpler cases lower isolated yields may be realized. 

We identified an efficient DDQ-mediated CDC reaction between IV-phenyl THIQ and nitromethane that provides access to a number of rare chiral vicinal diamines [via 27d, Scheme 11.22). ° In the course of this work we observed NMR spectroscopic evidence for the long-supposed iminium ion and noted the precipitation of a solid in the reaction mixture which when isolated and then dissolved led to the reaction product. Subsequent focus on this solid using elemental analysis led to its suggested identity being 26c, where an iminium ion paired with the anion of the DDQ reaction product (the dihydroquinone) and this salt precipitated with another molecule of the protonated dihydroquinone (DDQHa). The solid was successfully... 

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