[Dan]

I'm curious about the final step in this synthesis of Oxerine.

The general reaction is

ROBn --TMSI--> ROH                solvent: Chloroform

Unfortunately, the experimental for this step is very vauge. In fact, all they say is that the starting material was dissolved in chloroform, irradiated with ultrasound and then concentrated in vacuo and purified by PTLC. TMSI (trimethylsilyl imidazole) is only mentioned in the general scheme, not the experimental (?).

Now, I could see perhaps that:

ROBn --TMSI--> ROTMS --aqueous acidic workup--> ROH

but I think even this is odd, and there is certainly no mention of an aqueous workup.

Next thing is, I'm speculating with very limited knowledge of the use of ultrasound - the extent of my knowledge is "the molecules will be excited". Will this be a radical process? ie will the ultrasound promote homolysis?

Any thoughts?

[movies]

I think that TMSI in this case means trimethylsilyl iodide.  It's a pretty wicked Lewis acid with a decent nucleophile as well.  You can even use it to cleave methyl ethers sometimes.

[Dan]

Aah, yeah it is the iodide, I missed that. So, that would leave you with the silyl ether? Then I suppose there must be an acidic aqueous workup to yield the alcohol that just wasn't mentioned?

Thanks Movies

[movies]

Yeah, probably.  TMS tends to fall off...in general.