Dear Sel,

Oxidation of curcumin proceeds through a series of quinone methide and other reactive intermediates to form a final dioxygenated bicyclopentadione product. 

See the following paper. For viewing the oxidation scheme please use the link in the bottom of this message.

Biochemistry. 2013 Jan 8;52(1):221-7. doi: 10.1021/bi3014455. Epub 2012 Dec 26.

Oxidative metabolites of curcumin poison human type II topoisomerases.

Ketron AC1, Gordon ON, Schneider C, Osheroff N.

Author information

 http://www.ncbi.nlm.nih.gov/pubmed/23253398

Abstract

The polyphenol curcumin is the principal flavor and color component of the spice turmeric. Beyond its culinary uses, curcumin is believed to positively impact human health and displays antioxidant, anti-inflammatory, antibacterial, and chemopreventive properties. It also is in clinical trials as an anticancer agent. In aqueous solution at physiological pH, curcumin undergoes spontaneous autoxidation that is enhanced by oxidizing agents. The reaction proceeds through a series of quinone methide and other reactive intermediates to form a final dioxygenated bicyclopentadione product. Several naturally occurring polyphenols that can form quinones have been shown to act as topoisomerase II poisons (i.e., they increase levels of topoisomerase II-mediated DNA cleavage). Because several of these compounds have chemopreventive properties, we determined the effects of curcumin, its oxidative metabolites, and structurally related degradation products (vanillin, ferulic acid, and feruloylmethane) on the DNA cleavage activities of human topoisomerase IIα and IIβ. Intermediates in the curcumin oxidation pathway increased the level of DNA scission mediated by both enzymes ~4-5-fold. In contrast, curcumin and the bicyclopentadione, as well as vanillin, ferulic acid, and feruloylmethane, had no effect on DNA cleavage. As found for other quinone-based compounds, curcumin oxidation intermediates acted as redox-dependent (as opposed to interfacial) topoisomerase II poisons. Finally, under conditions that promote oxidation, the dietary spice turmeric enhanced topoisomerase II-mediated DNA cleavage. Thus, even within the more complex spice formulation, oxidized curcumin intermediates appear to function as topoisomerase II poisons.

For viewing the oxidation process please use the following link:

http://www.ncbi.nlm.nih.gov/core/lw/2.0/html/tileshop_pmc/tileshop_pmc_inline.html?title=Click%20on%20image%20to%20zoom&p=PMC3&id=3541001_nihms-431325-f0001.jpg

Hoping this will be helpful,

Rafik

The attached file may be helpful

I think what Rafik has replied is pretty precise. Now it is upto you to find out whether benzoquinone is finally produced or not.