L3 - Wittig and HWE

Question 1

What is used to deprotonate stabilised phosphane?

Answer 1

Strong base

NaOH / t-BuOK

Question 2

What is used to deprotonate unstabilised phosphanes?

Answer 2

Very strong base

BuLi / NaNH2 / LDA

Question 3

What type of control is the stereochemistry of the Wittig reaction under?

Answer 3

Kinetic control

Question 4

What is the Horner-Wadsworth-Emmons reaction (HWE)?

Answer 4

The reduction of a phosphonate stabilised carbanion with a carbonyl

Question 5

What is required for the HWE reaction?

Answer 5

Electron withdrawing group

Question 6

How are the HWE phosphonates required formed?

Answer 6

Nucleophilic attack of a trialkylphosphite

Question 7

How are the HWE phosphonates required formed?

Answer 7

Nucleophilic attack of a trialkylphosphite on an alkyl halide to give an unstable trialkylphosphonium.
Nucleophilic attack by the halide anion then causes dealkylation, forming a P=O, giving the phosphonate

Question 8

What type of base is needed to form the HWE phosphonate?

Answer 8

Strong base

nBuLi

Question 9

How do the pKa values of phosphonates compare to their corresponding ylides?

Answer 9

They are much higher

Question 10

Why are deprotonated HWE phosphonates good?

Answer 10

They are more nucleophilic so can react with less reactive carbonyls such as ketones

Question 11

What is the practical advantage of the HWE reaction?

Answer 11

The phosphate byproduct can be removed by washing with aqueous base