Iodo etherification

[Kaeroll]

Hi,

 

A synthesis my lecturer dubbed 'iodoetherification' cropped up this week. I can't find reference to it or anything much like it in my organic text; can anyone recommend a book or article with a decent explanation of it?

 

Cheers

Kaeroll

[UC]

Iodine is very poor at adding to double bonds, so perhaps the first two stages normally equilibriate, but don't proceed to full addition across the double bond. I'm just guessing at that, but that's probably why iodine is used instead of other halogens, which would readily add completely across the bond forming vicinal dihalides.

 

Iodolactonization is also known, where the alcohol group is replaced by a carboxylic acid. The iodine sources I'm seeing are N-iodosuccinimide, I2, or a mix of NaI and FeCl3 with solvents like acetonitrile and chloroform at 0C

 

I don't know how well this reaction would work intermolecularly, but my guess would be poorly.

Edited April 26, 2009 by UC

[Kaeroll]

Thanks for your reply and apologies for the delay in mine - it's crunch time yet again.

 

I spoke with my organic tutor about this and he suggested the same kind of mechanism as you. It's a shame it's nowhere to be found in the texts I have to hand (including one for the course this came up in). Just to make things simpler, the lecturer described the cyclisation (which was onto an alkyne, rathr than alkene) as 5-endo-dig, rather than accounting for the likelihood of this mechanism (which would be -trig, presumably). He also offered no explanation for the presence of iodine in the product.

 

Thanks again for your response. It does seem obvious now it's right before my eyes.

[UC]

Funny. I'd never even heard of Baldwin's rules until now. I suspect that if you were to move the alkyne one carbon closer to the alcohol group and throw an alkyl chain on the other end of it, you could get 5-endo-dig cyclicization via a similar mechanism, giving a 3-iodo-2,3-dihydrofuran ring.

Edited May 9, 2009 by UC

[Kaeroll]

Yes, that's the kind of example we were given, and was described as -dig when the mechanism is actually -trig. Go figure.

 

Baldwin's rules are something I had to look up myself - they've popped up a lot this semester and last (during topics on radical reactions, pericyclic reactions, heterocyclic synthesis - where iodoetherification came up - and others) but they've never been formally presented to us.

[UC]

Yes, that's the kind of example we were given, and was described as -dig when the mechanism is actually -trig. Go figure.

 

Baldwin's rules are something I had to look up myself - they've popped up a lot this semester and last (during topics on radical reactions, pericyclic reactions, heterocyclic synthesis - where iodoetherification came up - and others) but they've never been formally presented to us.

 

Well, based on the very short lived intermediate, it would be -trig, but if you consider only the starting material and the ending material, -dig is appropriate. I'm not sure which is technically correct.

[Kaeroll]

Well, based on the very short lived intermediate, it would be -trig, but if you consider only the starting material and the ending material, -dig is appropriate. I'm not sure which is technically correct.

Yeah, that was the distinction I was trying to make. I think it's dependant upon the mechanism rather than the apparent overall reaction, but I'm not sure. I'll have a gander in my textbook and see what Prof Clayden has to say...

[UC]

Yeah, that was the distinction I was trying to make. I think it's dependant upon the mechanism rather than the apparent overall reaction, but I'm not sure. I'll have a gander in my textbook and see what Prof Clayden has to say...

 

I sent my prof. an email as well. I have no idea when he'll respond since semester is over. I kind of get the feeling that nobody cares and since the -dig describes the whole reaction, not just a step, it would be presferred.