Organic chemistry

Hello!

Also I'm struggling with drawing a mechanism for the reaction of triflic acid/TfOH (CF3SO2OH) with NIS? I need to show how TfOH activates NIS as an I+ donor.

For part one, you're going to have to remove the Ac group first to get back the alcohol and then add the Bn protecting group. I think looking up acid/base catalysed ester hydrolysis (for step 1) and the Williams ether synthesis (for step 2) will be useful.

The triflic acid would protonate one of the O atoms in the imide thus weakening the NI bond as the lone pair on the N would be pulled towards the protonated carbonyl group.

Hi Oxazole,

Thank you for your reply! I was just wondering whether the group being attached if a cyclohexane chair structure would change things? (Hoping a picture has attached)

Thank you

No worries . I don't think the ring will throw up any problems - people have used Bn protecting groups on similar ring strucutres with excellent yields:

http://www.chem-station.com/en/reactions-2/2014/03/benzyl-bn-protective-group.html
https://www.thieme-connect.de/DOI/DOI?10.1055/s-1995-5259

TeachChemistry,

Thank you for your reply! To this post I have attached a picture with my interpretation of your words along with an alternative mechanism I'm a little sceptical about. Please could you tell me if I have done this correctly? As I'm not sure if showing the I+ being attached to CF3SO2OH is the correct way to show TfOH activating NIS as an I+ donor?

Thank you!

I don't buy the photochemical reaction here.

You have drawn the mechanism I suggested in the top part of your piece of paper except that I suggest the nucleophile would be the substrate that is being iodinated rather than the triflate.

http://pubs.acs.org/doi/abs/10.1021/jo00063a052
Suggests your intermediate is formed.

TeachChemistry,

Thanks for your reply again I got a little confused when you said the "nucleophile would be the substrate that is being iodinated rather than the triflate". After a bit of thought, I think another question (question attached along with what I think the answer is) would allow me to incorporate what you are saying. The question is to draw a mechanism for the conversion of 1 to 3 and 2 to 4, showing why the different protecting groups influence stereochemistry. I think what I have done has shown the nucleophile being iodated rather than the triflate but I was also wondering whether my interpretation of the mechanism is correct? I'm always unconfident when it comes to mechanims! Perhaps rightly so, I'm not sure!

Thank you!