Silicon in Synthesis 3 Flashcards
What is an allyl silane
An alkene but with a CH₂ between the alkene group and the silicon
How do allyl silanes react with elecleophiles
Using the Peterson Olefination to form an allyl silances requires two units of trimethylsilyl groups to form an allyl silane
What is the mechanism
- Eventually form a ketone which is a better electrophile than a ester
- strong Si-O bond drives peterson-olefination
We can also form allyl silanes using the wittig reaction with phosphorous ylides
- forms an oxophosphotane intermediate
- Way of making an allyl silane with an R group in the middle of a molecules, rather than just at the end
You can react a Allyl silane with iodine to form?
What is the product if an allyl silane reacts with R-X
TiCl₄ lewis acid
What is the product if an allyl silane reacts with an epoxide
TiCl₄ lewis acid
What is the product if an allyl silane reacts with an acyl chloride
TiCl₄ lewis acid
What is the product if an allyl silane reacts with an enone
TiCl₄ lewis acid
What is the intermediate for all these reactions?
What is the mechanism for an allyl silane reacting with an expoxide
What is the mechanism for an allyl silane reacting with a ketone to form a homoallylalcohol?
(same also applies for enone but attack on the C=C rather than C=O)
If we have more than one functional group in a molecule, and only want to react on of them, we need to….
… protect the other functional groups
We can protect an alcohol using…
How can we remove the protecting group one the reaction has occured?
a Silyl ether
using TBAF or a strong acid and water
What is the name of the following compound
TMS-OR
What is the name of the following compound?
TBDMS-OR
or
TBS-OR
What is the name of the following compound
TIPS-OR
What is the name of the following compound?
TBDPS-OR
Which is the most stable silicon protecting group in acid
Increasing stability in acid from left to right
TMS is only stable in 0.5M HCl
While TBDPS is stable in 5M HCl
