Hi – you can use nonpolar solvents such as diethyl ether or benzene but you don’t get catalytic turnover. That means you have to use stoichiometric OsO4. The eventual product is an osmate salt that has to be treated with a reductant like bisulfite or H2S to get back the diol. Since osmium is very expensive, this is not advised.

The NMO and water helps with catalytic turnover. There are several important catalytic cycles going on.

1) OsO4 (osmium VIII) performs a dihydroxylation on the alkene, resulting in an osmate ester [Osmium (VI) ]
2) This osmate ester has to be hydrolyzed to give the osmate salt.
3) The osmate (VI) salt is re-oxidized to osmium tetraoxide (Os VIII) with NMO.

[If you want to be picky, coordination of amines like N-methyl morpholine to osmium also helps, increasing the rate of dihydroxylation versus the absence of amines]

Water serves several purposes. The first purpose is to act as a solvent for the highly polar osmate salt and NMO; the second is to act as a nucleophile (under mildly basic conditions, there is likely some HO(-) around) to cleave the osmate ester.

For more commentary, the original paper is here (https://www.sciencedirect.com/science/article/abs/pii/S0040403900780932) – I don’t have full access.

Hi – great questions. Start with neutral osmium having an oxidation state of zero. Then subtract 1 for every bond to a more electronegative atom (O). In OsO4 there are eight. In the osmate ester there are six bonds to oxygen. This accounts for the difference in oxidation state – it has gone from Os(VIII) to Os(VI)

What happens when the lone pair goes into Os during the [3+2] is that there are an extra pair of electrons on osmium that weren’t there before. We generally don’t draw the lone pairs in on transition metals (because there can be a lot!). But if we know the oxidation state, we can figure it out. The oxidation state is now two less due to that lone pair.

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.