[owk9688]

Hello,

I've never done an oxidation of an alkene before and have also never used mCPBA. The reaction I'm attempting now is to take ortho-allyl Phloroglucinol and oxidize the terminal alkene into an epoxide (so that eventually one of the phenols can open it and I can form a bicyclic structure. It seems straighforward and theres precedent with doing the reaction with ortho-allyl phenol so I feel like it should work and I must be doing something wrong.

Im adding the mCPBA all at once to a stirred solution of my allyl phloroglucinol in Room temperature DCE. The reaction mixture turns deep brown within about 20 seconds after I've added the mCPBA.  My TLC shows complete dissapearance of my product at only 1 hour but the mixture is still this awful looking dark brown. In the crude HNMR I cant see anything that resembles my product. Is there something I'm doing wrong? Should I not be adding the mCPBA all at once?

Any help or suggestions would be appreciated. Thank you!

[Doc Oc]

Did you also run TLC of the mCPBA and benzoic acid for reference? How old is your mCPBA and how has it been stored?

[owk9688]

I did not run the spots of the mCPBA sample on the TLC as well. I'll definietly do that when I try this again. The mCPBA was about a month old and had been stored in the refrigerator but we had a malfunction that caused it to not be cold for a full week. Thats the only thing I can think of thats been out of the ordinary for our storage of it.

[wildfyr]

Could you clarify the starting material a little more? Its a benzene ring with a phenol at 1 and 3, and an allyloxy at 5?

Perhaps you should do it at 0°C and add the MCPBA slowly. Formation of brown garbage smells of polymerization. Also, doing this under air and water free conditions if it isn't already is the first thing I do when a reaction is misbehaving.

My TLC shows complete disappearance of my product at only 1 hour but the mixture is still this awful looking dark brown.

Do you mean starting material disappears after 1 hr? if the product is showing up and then disappearing then I suspect polymerization even more. Poly-phenols like this have funny properties.

My hypothesis is that the phenols are attacking the epoxide intermolecularly via acid-catalyzed epoxide ring opening. The acid catalyst is coming from the benzoic acid byproduct.

One trick I do know though, is for workup, you should first do an aqueous sodium bisulfite wash to reduce the leftover MCPBA to its benzoic acid. Basic workups like aq bicarb don't do a good job of removing MCPBA, but do remove the benzoic acid derivative nicely. I fought this problem for a damn week before an older student dropped a knowledge bomb on me about it.

[owk9688]

Sorry. I’m not sure how to post images here. My substrate is a benzene with phenols at the 1,3, and 5 positions, and an allyl at the 2 position. I suppose side reactions are possible considering aromatic system has 3 strongly activating substituents and one weakly activating one. I will try running it at 0 Celsius and adding the mCPBA portionwise and see if that helps. If not, I may just have to try hydrogen peroxide maybe.

Thank you so much