[yesway]

Hi,

If I subject a compound with defined absolute stereochemistry at a lot of stereogenic centres (one enantiomer only) to an asymmetric reaction, I will create (in my case) one new stereogenic centre. To describe the stereoselectivity accurately, is it right to describe the products in terms of diastereomers (d.r.) or in terms of the asymmetric reaction itself (e.r.)? I'm tending towards d.r., because the resulting product mixture will be diastereoisomers, not enantiomers, but I'm a bit confused.

Thanks

[discodermolide]

I would say dr in this case. But you can get >500:1 dr, meaning more or less enantioselective

[Dan]

If the reaction produces diastereomers, then use d.r.

If the reaction produces enantiomers, use e.r.

It is possible that both apply, e.g. the formation of a chiral compound with two (or more) new asymmetric centres from achiral starting materials.

In your case, it sounds like it is not possible to form both enantiomers of the product because the absolute configuration(s) that were present in the starting material are preserved in the products. Unless the optical purity of your starting material could be altered under your reaction conditions, to use the term enantioselective is meaningless.

>500:1 d.r. ≠ "more or less enantioselective" - d.r. and e.r. measure completely different things

[yesway]

Thank you both - indeed the "old" stereogenic centres are preserved in my case, I should have given that information!