NMR question

[kristina221]

Here is the spectra of compound X5 and what I think might be X5. Peaks at 163 ppm (13C) and 7.5 ppm(1H) are the fact that is confusing me. No, there is no molecular formula or MS. I understand the last step, but I'm confused by X6 nmr too, because those peaks appear again. The only explanation I came up with is that the H on the carbon atom between the OH and Br is so strongly deshielded.

 

Or is it 2-bromo-2,3,4,5-tetrahydropyridine-3,4-diol

[Horza2002]

I would be extremly suprised if that proton was that high. Protons above 7ppm are either aromatics or they are aldehyde (unless there are some interesting ring systems). Can you put what you propose for X1-6 so we can see if your along the right lines. I've come up with a structure but I want to see what you;ve got so I can give you the helping nudges.

[kristina221]

X1

X2

X3

X4

or for X5

X6

 

I would be extremly suprised if that proton was that high. Protons above 7ppm are either aromatics or they are aldehyde (unless there are some interesting ring systems). Can you put what you propose for X1-6 so we can see if your along the right lines. I've come up with a structure but I want to see what you;ve got so I can give you the helping nudges.

 

I'm aware of that fact. That's why I'm asking

[kristina221]

in the end i decided to go with (3S,4R)-3,4,5,6-tetrahydropyridine-3,4-diol as x5

[Horza2002]

First of all, I'm sorry I didn't reply, I totally forgot about it! So sorry!!

 

One thing you need to be careful of is that you can't predict what enantiomer you will get, there is no chiral enviroment to direct the attack and so you will get a racemix mixture. While in principle, the opening of the epoxide should give you an anti relationship to the resulting hydroxyl group, in this case, the piperidine nitrogen will scramble is and so will give a mix of syn and and anti bromo/hydroxy group.

 

I am very confused by the proton NMR as well though...it doesn't seem right to me, unless im missing something obvious. Another thing that annoys me about these schemes is that the reagentss they choose can lead to several different products.

[kristina221]

i assume that the 160 and 7.5 shifts are for the imine c atom

[Horza2002]

That would make sence yes. Typically carbons up that end spectra are normally carbonyls so an imine would be there as well. Aldehyde protons are typically around 9ppm so an imine one would be a little lower but also higher than expected. That is the product I came to aswell