Boron Chemistry Flashcards
Why does boron have lewis acid properties?
Because of it’s lone p-orbital
[He] 2s² 2p¹
What is boron like in terms of electronegativity?
- Not very polarised (often more δ⁺)
- Meaning its relatively stable
How does the following reaction occur
- Addition of two alkenes onto borane
Why is the following reaction regioselective and steroselective?
- Regioselective: hydride goes where positive charge developing where alkene is most stabilised
- AND sterics dictates that the larger the BR₂ goes to the least hindered position
- Stereoselective: In this case the cyclopropyl group blocks one face, leading to a single enantiomer product
The following reaction is an oxidation of alkyl boranes to an alcohol
How does it occur?
Migration of alkyl group to the oxygen, peroxide bond breaks
The sterochemistry at carbon is retained
Silicon can also undertake a peroxide mirgration reaction driver by weak O-O bond
How does this reaction occur?
Carbon can also undertake a peroxide mirgration reaction driver by weak O-O bond
How does this reaction occur?
Boron in the following reaction is a lewis acid
What is the mechanism for this?
Boron also acts as a lewis acid in the following aldol reaction
What is the mechanism?
(note: Cy= Cyclohexane, Tf= triflate - OSO₂CF₃ - v good LG)
The transition state for the following reaction is show below
Show how the arrangement of the hydroxyl and methyl group is affected in the chair transition state
The following reaction uses an allyl boron reagent
What is the mechanism
- HOMO of alkene is raised
- AND lewis acid activation of aldehyde lowers the LUMO
Explain the diastereoselectivity of this reaction of boron allylation
