uemura, since you seem to have asarone in relatively large amounts, could you give the oxidation with dichromate a try?
(see http://rhodium.lycaeum.org/chemistry/aldehyde.txt (http://rhodium.lycaeum.org/chemistry/aldehyde.txt)
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I think the question rather is why is the aldehyde formed in such a "high" yield when the basic KMnO4 evidently is able to oxidize it further to the aldehyde? Could the reaction conditions be altered to give an even higher yield, and in that case how?
Someone really should extract the final solution with DCM and rotovap it down and run a gc/ms on it to see what is formed besides the aldehyde. It is probably not only the acid, as the authors of the orignal article notied that very little of the acid could be isolated from the filtered mixture.
http://rhodium.lycaeum.org (http://rhodium.lycaeum.org)