Reagent for protection of aldehyde groups as 2-substituted-1,3-dimethylimidazolidines, e.g. by azeotropic dehydration with benzene. The derivatives are stable to n-BuLi and LDA, and can be cleaved by acid hydrolysis, or in high yield by quaternization with MeI and mild hydrolysis: Tetrahedron, 41, 3803 (1985). With aromatic aldehydes, the imidazolidine derivatives are activated to ortho-lithiation, providing a route to o-substituted benzaldehydes: J. Org. Chem., 44, 2004 (1979).
