I haven't experienced this, but it could still be water. Did you activate the sieves prior to use? Store your solvents over activated sieves for a while before use. Note that they take several hours to absorb water, it doesn't happen instantaneously.

In terms of O2, sparge the system with N2 or Ar or another inert gas for a while before starting a reaction. If you freeze-pump-thaw the system, if you have a leak it will suck air in because its a vacuum. 

Best of luck! 

thanks for your advices. I will check them right away 

Hey,

Here are really good references for your reaction:

http://pubs.acs.org/doi/abs/10.1021/jo00115a018

http://pubs.acs.org/doi/abs/10.1021/jo961607u

If you're using Rh catalysed C-H insertion, it may not work. I worked on a very similar project, my diazo being subsituted with an ester on one side and a phenyl, benzyl or styryl on the other side. And I have not be able to do the cyclization, the carbene resulting of the degradation of the diazo by the Rh catalyst was not reactive enough. Your oxidation problem may come from a carbene that is not reactive enough to insert into a C-H bond.

Also Kyle A. Grice gave you good advice for deoxygenating a solution, I do that and it works every time.

Ask me if you need more information.

Dear  Dinhuv

You must conduct the rection under inert gas like Nitrogen or Argon and you can follow the following paper.

https://www.researchgate.net/go.Deref.html?url=http%3A%2F%2Fpubs.acs.org%2Fdoi%2Fabs%2F10.1021%2Fjo00115a018

Good Luck

Prof. Dr. Talaat El-Emary