Ph2p(O) Group For Protection Of Terminal Acetylenes

A protecting group Ph2P(O) for terminal ethyne was newly developed. This protecting group can be introduced readily to terminal ethyne by CuI-catalyzed phosphination and subsequent oxidation with H2O2. Ph2P(O)-protected ethynes remained intact in Sonogashira coupling, and their high polarity enabled easy separation of the desired coupling product from by-products. By treatment with t-BuOK, Ph2P(O)-protected ethynes were transformed to the corresponding terminal ethynes.