[cseil]

Hi, I found this exercise.
He asks me to find out why the product has the same configuration.

There's a carbocation and a sp2 carbon, so I can't understand why the oxygen attacks only from one side of the plane.
Can you help me please?

[discodermolide]

Try diazotisation of the NH₂ as a start, then think about how you might retain the configuration.

[mjc123]

The product you have drawn has inversion of configuration. Is that right?

[cseil]

The product you have drawn has inversion of configuration. Is that right?

Yes, S to R.

The start is the diazotisaton, but it's an aliphatic compound so the N2 goes out and a carbocation is formed. Is that right?
This was my start.

[Dan]

it's an aliphatic compound so the N2 goes out and a carbocation is formed.

How do you think the carbonyl adjacent to your predicted carbocation would affect its stability?

[orgopete]

Hint, since the stereochemistry is not lost, a carbocation is probably not an intermediate. Hint #2, alpha-???

[cseil]

The carbocation is not stable at all considering the presence of C=O. But I cannot understand how to continue. I can see only the formation of the carbocation and the attack from the O-. Otherwise the lactone is not formed.

[discodermolide]

Try making the alpha lactone, and decide what this does to the stereochemistry. then see if you can convert that to the desired product