[allthingschm]

Hi! I'm confused by what the exact definition of double stereodifferentiation is. I read in the Masamune 1985 paper on this that it means the reaction of 2 homochiral ligands, a substrate and a reagent to add new chiral centres to a chiral substrate. However, in the catalytic osmylation paper i'm reading up, the double stereodifferentiation reaction stated only involves a chiral substrate, osmium oxide and a chiral ligand dihydroquinidine 4-chlorobenzoate (DHQD), there is no second chiral ligand. Can anyone give me a clear definition of double stereodifferentiation and how it works? Also, are there alternatives to DHQD i.e. similar chiral ligands for osmylation? Also, what are some examples of slow addition conditons? Are low temperatures the only variable factor? Thanks

[Dan]

Hi! I'm confused by what the exact definition of double stereodifferentiation is. I read in the Masamune 1985 paper on this that it means the reaction of 2 homochiral ligands, a substrate and a reagent to add new chiral centres to a chiral substrate.

It is the reaction of two homochiral reagents. The homochiral reagents could be a complexes containing chrial ligands, but not necessarily. There need not be any ligands involved at all - see scheme 5 of Masamune's paper (ACIE, 1985, 24, 1-30) for examples of chiral aldehydes reacting with a chiral enolates with no additional chiral ligands.

However, in the catalytic osmylation paper i'm reading up, the double stereodifferentiation reaction stated only involves a chiral substrate, osmium oxide and a chiral ligand dihydroquinidine 4-chlorobenzoate (DHQD), there is no second chiral ligand.

Draw the reaction or provide a reference please.