Concave Reagents. 20. Sterically Shielded m-Terphenyls as Selective Agents in General Protonations(1).

New m-terphenyls with acidic substituents in the 2'-position have been used in general protonations leading to reagent-controlled selectivity enhancements: up to 96:4 for the gamma/alpha-protonation of unsymmetrically substituted allyl anions, up to 97:3 for the protonation of cyclohexyl anions generating preferentially the thermodynamically less stable cis-products. In order to allow a general, reagent-controlled protonation the acidity of the protonating agent should be as low as possible.