Problems and exercisesLewis-acid-catalyzed aldol addition (Mukaiyama)
Exercise 1
Why does a silyl enol ether not react with an aldehyde at −78 °C, while it does when TiCl4 is added? What advantage does this reaction have over the aldol addition of a lithium enolate?
Exercise 2
With BF3·OEt2 as the Lewis acid, the E and Z silyl enol ethers of the same ketone give similar proportions of the syn and anti aldols with benzaldehyde. What does this result indicate about the transition state?