Organocatalyzed Direct Aldol Reaction of Silyl Glyoxylates for the Synthesis of α‑Hydroxysilanes

A novel organocatalyzed
direct aldol reaction of aldehydes to silyl
glyoxylates is disclosed. This method provides an efficient route
to α-hydroxysilanes with excellent enantioselectivities (up
to 99% ee) and high diastereoselectivities (up to >20:1 dr). In
the
new activation model of silyl glyoxylates, the hydrogen bond is critical
to the reaction. A carbonyl group directly attached to silicon in
acylsilanes could be activated by coordination to the proton of hydroxyl
and carboxylic acid via a hydrogen bond. Moreover, commercially available cis-l-4-hydroxyproline is an ideal organocatalyst
for activating both aldehydes and acylsilanes.