text: Cyclic α,β-unsaturated ketones are the most commonly employed substrates for vicinal difunctionalization. They tend to be more reactive than acyclic analogues and undergo less direct addition than aldehydes. Amides and esters can be used to encourage conjugate addition in cases when direct addition may be competitive (as in the addition of organolithium compounds).
  Because the addition step is highly sensitive to steric effects, β-substituents are likely to slow the reaction. Acetylenic and allenic substrates react to give products with some retained unsaturation.