What is this functional group, and how do you make it

[CrimpJiggler]

On an exam question recently, I had to perform a retrosynthesis on a molecule and it had this functional group on it:

it took me by surprise. I decided to cleave the whole thing off, and replace it with a double bond (cuz I know you can make cis diols from double bonds) then things seemed to fall into place because the double bond let me do a retro diels alder and finish the question, but I couldn't explain how to make that double oxygen thing. I said you could make it with an osmium tetroxide catalysed reaction, but that doesn't explain the t-butyl group. After the exam, my classmates said it was an acetal protected carbonyl group but how can it be an acetal if the oxygens are attached at different carbons?

 

[jbsteele]

The functional group you are referring to is an acetal protected aldehyde. An acetal is a compound that contains two alcohol functional groups attached to the same carbon atom. In this case, the two alcohol functional groups are attached to different carbons, but these groups are held together by an ether linkage, which is why it is referred to as an acetal. The t-butyl group serves to protect the aldehyde from reacting with other molecules before the reaction is carried out. Osmium tetroxide catalysis can be used to cleave the acetal and free the aldehyde, allowing it to react.