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Results tagged with stereoselectivity
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user 21296
For questions about reactions that favour the formation of one or more stereoisomers.
8
votes
Why does acetate aldol with Evans auxiliary give almost no diasteroselectivity?
1. The acetate aldol reaction
Before looking at selective variants, its worth pointing out what an acetate aldol is.
An acetate aldol (below), is the simplest kind of aldol in which the β-hydroxyketon …
- 17.2k
15
votes
Accepted
Stereoselectivity of dihydroxylation with osmium tetroxide
Dihydroxylation responds to steric effects and proceeds at less hindered positions. What will be the major product in the following reaction if the reagent used is osmium tetroxide followed by sodi …
- 17.2k
4
votes
Why do Zr, Sn, and Ti enolates form syn aldols selectively?
For most aldol reactions, the relative 1,2-diastereoselectivity is a consequence of the enolate geometry.*
Both tin and titanium enolates are easily formed, and have been shown to exist predominantly …
- 17.2k
8
votes
Stereoelectronics of the Houk model
1. Origins of the Houk model
The initial idea behind the Houk model was infact provided by Kishi, who proposed that alkenes with a chiral centre on the adjacent carbon adopted a 'reactive conformation …
- 17.2k
5
votes
Chelation-controlled aldol: why is the α substituent pseudo-axial?
Having the methyl group psuedo-axial means that when the nucleophile approaches, the transitiation state is chair-like. The energy penalty for having the methyl group initially in the less favourable …
- 17.2k
22
votes
Why do we get slightly more inversion product than retention product in SN1 reaction?
It is well known that SN1 reactions often give incomplete racemisation:
Although many first-order substitutions do give complete racemization, many others do not. Typically there is 5–20% inversion, …
- 17.2k