Sciencemadness Discussion Board - Addition elimination mech question

Addition elimination mech question

methylene_beam - 6-3-2012 at 10:43

hello everyone one,

I have attached a proposed mechanism for the formylation of a purine.

I am generating the I^3 species in stichu to form the more favored N-iodo species which should activate the 8 position toward addition of a strong nucleophile. my question is concerning the mech can someone tell me if I am going to the right methodology.

(note chem sketch wont allow me to make CO)

formyl caffiene.bmp - 627kB

methylene_beam - 6-3-2012 at 11:09

correction: the second intermediate should not have a double bond in the imidazole ring.

rather showing electron migration to the nitrogen

[Edited on 6-3-2012 by methylene_beam]

GreenD - 6-3-2012 at 11:25

make the picture smaller, add the correct arrows in chem draw. this is a very ugly mechanism!

ThatchemistKid - 6-3-2012 at 11:41

I can't quite tell but it seems you are trying to take away electrons from an already positively charged oxygen, that isnt going to work.

methylene_beam - 6-3-2012 at 12:30

Quote: Originally posted by ThatchemistKid

I can't quite tell but it seems you are trying to take away electrons from an already positively charged oxygen, that isnt going to work.

I am attempting to show the carbonyl carbon(from CO) picking up the imidazole proton allowing for the aldehyde functionality and the return of its aromatic state by ejection of the I- on the nitrogen.

The black dot represents the carbonyl carbon.
1) positively charged oxygen attacks the carbonyl carbon.
2) the aromatic proton eliminates
3) elimination of the aromatic proton causes re formation of the aeromatic ring eliminating the N-iodo intermediate.

untitled.bmp - 357kB

[Edited on 6-3-2012 by methylene_beam]

Nicodem - 7-3-2012 at 09:37

I'm sorry to tell you that not much of what you depicted makes sense (to me). Despite your poor skills in using structure drawing software and unawareness of the meaning of mechanistic arrows, I understood that what you want to describe is a hypothesis that I2 could catalyze the formylation of caffeine with carbon monoxide. You seem to believe that I2 is inert to CO at the reaction conditions (without giving a reference). Thus, the carbocation generated by the electrophilic attack of the iodine at the nitrogen would in your (referenceless) opinion of all things react with the carbene (CO) rather than the iodide (admittedly this is reversible) or any other nucleophile present in the reaction medium (possibly irreversibly). Such a reaction would then give an acylium cation which is quite thermodynamically uphill and also very reactive. However, you seem to (referencelessly) believe that this species would not react with any of the plenty of nucleophiles present in the medium before it would have the time to undergo a 1,2-hydride shift to give the formyl derivative of caffeine. Is this what you are trying to describe and ask about? Well, I do not know if it works, but I have an irrelevant opinion about it.

PS: Please open referenceless threads only in the Beginnings section.

methylene_beam - 7-3-2012 at 12:08

Quote: Originally posted by Nicodem

I'm sorry to tell you that not much of what you depicted makes sense (to me). Despite your poor skills in using structure drawing software and unawareness of the meaning of mechanistic arrows, I understood that what you want to describe is a hypothesis that I2 could catalyze the formylation of caffeine with carbon monoxide. You seem to believe that I2 is inert to CO at the reaction conditions (without giving a reference). Thus, the carbocation generated by the electrophilic attack of the iodine at the nitrogen would in your (referenceless) opinion of all things react with the carbene (CO) rather than the iodide (admittedly this is reversible) or any other nucleophile present in the reaction medium (possibly irreversibly). Such a reaction would then give an acylium cation which is quite thermodynamically uphill and also very reactive. However, you seem to (referencelessly) believe that this species would not react with any of the plenty of nucleophiles present in the medium before it would have the time to undergo a 1,2-hydride shift to give the formyl derivative of caffeine. Is this what you are trying to describe and ask about? Well, I do not know if it works, but I have an irrelevant opinion about it.

PS: Please open referenceless threads only in the Beginnings section.

I really don't understand where the condescending nature of this reply is coming from. If i wanted to talk to insecure scientists I would go to academia with my questions.

anyway, I know people have been shitting on me about not using a program to draw these structures....I am sorry deal with it you know what i am trying to depict. And why would i use anything but doubles headed arrows?

Quote:

You seem to believe that I2 is inert to CO at the reaction conditions (without giving a reference). Thus, the carbocation generated by the electrophilic attack of the iodine at the nitrogen would in your (referenceless) opinion of all things react with the carbene (CO) rather than the iodide (admittedly this is reversible) or any other nucleophile present in the reaction medium (possibly irreversibly).

I am gong off the methodology that you posted in about one of my threads. and I said in that thread that the I3 species didn't react and returned starting material. I am going off your methodology presented and adding a more reactive nucleophile.

remember when you posted this??
http://www.sciencemadness.org/talk/files.php?pid=236202&...

You told me(in the other post) to use an inert solvent. dont you think thats what i am doing???

Quote:

However, you seem to (referencelessly) believe that this species would not react with any of the plenty of nucleophiles present in the medium before it would have the time to undergo a 1,2-hydride shift to give the formyl derivative of caffeine.

you keep mentioning that i don't have references.... of course i don't thats why i am asking the question lol. I am hoping someone with mechanistic knowledge can simply be like.

"no that wont work cause of ABC"
or
"maybe give it a try tell us what happens"

if iodo-phosgene in generated in situ it would only make the carbonyl carbon more reactive. maybe forming the polymerized product.

edit: why was this moved to "beginings" this subject matter is farm from that. now people arent going to read this, thanks........

alls i wanted was a yes or no. Its a shame when egos get involved

[Edited on 7-3-2012 by methylene_beam]

Nicodem - 8-3-2012 at 09:53

Quote: Originally posted by methylene_beam

anyway, I know people have been shitting on me about not using a program to draw these structures....I am sorry deal with it you know what i am trying to depict. And why would i use anything but doubles headed arrows?

It's obvious I'm talking to my self here, given that evidently you did not even bother to carefully read my reply above, but I will nevertheless try again. Like I said, I tentativelly understood your hypothesis even though you are unable to depict it or use mechanistic arrows. The problem you face has nothing to do with your drawing skills or rules in regard to arrow use. Your major problem is your disregard of the scientific method. You propose a mechanism for a reaction that does not even exist. What is worse, your hypothesis is not based on a single reference! That is not even a hypothesis any more. Regardeless of what you think, I'm actually trying my best to help you. The problem is that you are unable to accept any help for which you would have to pay with discipline, work and devotion. You want something, but you don't want to pay for it. So, who is having an ego problem here?

Quote:

Like it was already obvious to me at the time I wrote that reply, you misinterpreted what I wrote. Besides, since when is carbon monoxide a more reactive nucleophile than iodide, water and other things that you would want to have in the reaction mixture? Do you have a reference for that?

Quote:

You told me(in the other post) to use an inert solvent. dont you think thats what i am doing???

I said that it is advisable to use an inert nonucleophilic solvent if you want a higher chance of success. But on the other hand, you don't propose any reaction conditions for the non-existing reaction you propose in this thread. We are only left to guess you are talking about aqueous conditions due to your mention of the triiodide anion. Water is not a nonnucleophilic solvent.

Quote:

you keep mentioning that i don't have references.... of course i don't thats why i am asking the question lol. I am hoping someone with mechanistic knowledge can simply be like.

Now, what was that about? You want a scientific comment in regard to a poorly presented referenceless hypothesis of an imaginary reaction and you get pissed because you didn't understood the reply? What's worse, you don't even find all this absurd.

Quote:

"no that wont work cause of ABC"
or
"maybe give it a try tell us what happens"

Exactly the kind of reply that I gave you already. Since you are obviously not going to do any experimental research, you are forced to try and understand what that ABC I told you means. Obviously, this is not going to happen unless you do some literature search and reading. Coincidentally, that is exactly my final goal.

Quote:

edit: why was this moved to "beginings" this subject matter is farm from that. now people arent going to read this, thanks........

I moved the thread here so that you would be given a chance to learn step by step, rather than to just read replies without actually reading them.

methylene_beam - 9-3-2012 at 11:21

I am done with this place. This forum is for drug cooks and old guys with a chip on their shoulder. I have asked simple questions about things I am curious about and have been meet with hostility the entire time.

I have read other posts you have been in nicodem and your an asshole bro. see ya

zoombafu - 9-3-2012 at 11:57

Without heads on the curly arrows, there is no way to show which way the electron is flowing. Nicodem does have a point there.