[Rutherford]

The problem is attached. What will be the major product of the reaction D? The first structure corresponds to the usual condensation product, but I suspect that something else will happen here. I don't see a way for the third structure to be produced so I exclude it. How to decide between the second and the fourth structure?

[discodermolide]

The second structure seems to be very strained. I would go for the β-lactam.

[discodermolide]

The NMR also fits quite well to the last structure.

[Rutherford]

Yeah, the strain is probably causing instability of structure 2. I will try to work out which hydrogen would correspond to which line in the NMR.

[discodermolide]

That should not be too difficult

[Rutherford]

I did it, but I suspect whether it is correct. The two hydrogen in alpha position to the carbonyl group have 2.6-2.9 ppm but that seems too small, as they are so close to oxygen. In the hydrazyde the alpha hydrogen has a ppm of 9.0. How?

[Rutherford]

I think that these are disatereotopic hydrogens, not in the same plane with the oxygen atom.

[discodermolide]

They are diastereotopic one is up the other down.
The imine H is at 9.6. Just like an aldehyde.

[Rutherford]

Perfect, I think I understand this. Thanks for the help.

[Rutherford]

Why don't the 5.5 and 9 ppm protons split each others signal (spectrum of the hydrazyde)?

[discodermolide]

Sorry don't follow your question.

[Rutherford]

Why aren't they coupling?

[discodermolide]

This compound?


I don't think the alpha proton to the C=O is at 9 ppm. In the spectrum you posted where did this come from? My ChemDraw predicts a doublet for both the protons on the C=C.

[Rutherford]

I found that I got the hydrazyde structure wrong, it's the attached one. Now to what protons should the singlets be assigned?

[discodermolide]

How about the two NH protons. The signals are quite broad.