fixed! thanks for the catch. James

Without knowing the structure, it’s hard to say. Is it an alpha, beta unsaturated aldehyde? Epoxidation may work, but then again peroxide may end up oxidizing your aldehyde.

Aldehydes are some of the most sensitive functional groups to oxidation and other side reactions. I would generally suggest they are protected unless you have some strong reason for believing it would not be affected by the OsO4 or its co-oxidant.

I think I found a way how to this, without protecting the aldehyde. I would appreciate to get your opinion

Stage 1: reaction with peroxide to get epoxide
Stage 2: acidificaion

Hi Ptachia – I would not do a dihydroxylation with an unprotected aldehyde. Too many things can go wrong. Either keep it at the protected alcohol stage and then oxidize up afterwards, or protect the aldehyde as an acetal and then perform the dihydroxylation.

If we have a molecule which contain both alkene and aldehide’and we want to prepare diol. will osmium tetraoxide oxidize the aldehide? If yes can you suggest me how to get the diol without oxidizing the akdehide?

Whether you get one product or a mixture of enantiomers/diastereomers will depend on the alkene you start with.

Dihydroxylation of ethene would only give one product, for example.

The reaction itself is stereoselective. Starting with cyclohexene you get one product – cis 1,2-cyclohexane diol, and none of the trans. If you obtained a random *mixture* of cis- and trans- 1,2-diols from cyclohexene, then it would not be stereoselective.

This is going beyond what you asked, but not only is this reaction stereoselective, it is stereospecific.
Here’s why.
Take two alkenes that are diastereomers. cis but-2-ene and trans but-2-ene.
Now treat each with OsO4.
The cis but-2-ene will give a single product (S,R)-2,3-butanediol (meso).
The trams but-2-ene will give a racemic mixture of diols. (S,S)-2,3-butanediol and (R,R)-2,3-butanediol. These are each diastereomers of (S,R)-butanediol.

So two diastereomeric alkenes give two diastereomeric products. That’s the IUPAC definition of stereospecific.

Great question. It just doesn’t. Although it will react nicely with diols.