Problems and exercisesRegioselectivity and enantioselectivity in ketone alkylation
Exercise 1
Give the main product of 2-methylcyclohexanone with: (a) LDA, THF, −78 °C, then allyl bromide; (b) Me3SiCl, Et3N, refluxing DMF, then MeLi and finally allyl bromide.
Exercise 2
Why is the thermodynamic enolate the more substituted one? Which conditions allow the two enolates to equilibrate?
Exercise 3
In the Evans alkylation, which three roles does the chiral auxiliary play? How is it removed at the end, and why is the configuration of the new stereocentre not lost?