Patemo-Bilchi Reactions

The diastereoselectivity dropped drastically in presence of protic methanol and totally disappeared for the corresponding silyl ethers. These data are in agreement with the presence of a hydroxy directing effect in the Patemo-Bilchi reaction. Threo stereoisomer can be favored through the formation of an hydrogen bond between triplet excited benzophenone and the substrate in the exciplex, while the formation of the erythro stereoisomer would be less favored due to allylic strain (Scheme 3.41). 

---