Useful Organocatalyst for Acid-free Acetalization

1,3-Bis[3,5-bis(trifluoromethyl)phenyl]thiourea (1) is a useful organocatalyst for acid-free acetalization. Acidic catalysts, such as p-toluenesulfonic acid, are generally needed for acetalization. However, the use of this catalyst makes it possible to acetalize carbonyl compounds under neutral conditions, affording the corresponding acetal compounds in moderate to high yields. In particular, it is useful for acetalization of carbonyl compounds bearing acid-sensitive groups, such as the TBDMS protecting group.