Asteltoxin, isolated from the cultures of Aspergillus stellatus, exhibits a potent inhibitory effect on the activity of E. coli BF1-ATPase. During S. L. Schreiber’s synthesis of asteltoxin, compound 1 was treated with a strong base to form anion 2 (J. Am. Chem. Soc. 1984, 106, 4186–4188):
(b) Determine whether each of the following bases would be suitable for deprotonating compound 1 and explain your decision in each case: (i) NaOH, (ii) NaNH2, or (iii) CH3CO2Na.
Alright. Now, let's go ahead and figure out the sodium hydroxide, sodium amide or a oxide can go ahead and deprotonate this hydrogen here, okay? To remove that hydrogen but in order to do that we need to know our pka's, right? We don't the pka's for these, right? Well, the conjugate acids no problem but we're not really entirely sure about the pKa of this molecule here, right? So guys, this is where experience might definitely help a little bit, right? So we've got something that looks a little bit familiar to me, it looks like a more complicated version of a phenol is something called tautomer but don't worry about that, you'll learn about that later. So, phenol looks like this, we've got a benzene ring, right? With our double bonds here, you might also seen it, you might have also seen it drawn like this because it's a highly delocalized ring, right? So we've got something like this and we've got our OH up here, our alcohol coming off directly from our benzene, and guys what I know about that molecule is that it can resonance very similarly to this molecule, okay? And it's also got a pKa of about 10, so we should expect that this molecule over here, this hydrogen should have a pKa of about 10, alright? So, we need to have a base that's going to have, the whose acid has a conjugate base of conjugate acid pKa, right? The conjugate acid pKa of above 10, so let's take a look and see if we have that. First let's go ahead and draw out our conjugate acid, here we know that sodium hydroxide conjugate acid is water NaNH2 would be NH3, CH,CH2O, right? That's a ethoxide, we know that it's just going to be ethanol, so I'm just going to go ahead and draw it out like that, guys, what do we know where pKa is for water? we know it's going to be 16, ammonia 38 and alcohol we know it's going to be about 15.7. So, are any of these above 10? absolutely, right? So guys actually every single one of these can go ahead and deprotonate this molecule here. Alright not so bad, right? It's a little bit weird you just have to know, it helps to know a little bit about benzene and phenol and stuff like that. Alright guys, let's move on.