Transition Metal-Promoted Synthesis of Functionalized and Unfunctionalized Pyridylallenes

Abstract

The S_N2′-substitution of several functionalized and unfunctionalized pyridyl-substituted propargylic acetates with the magnesium cuprate MeMgCl·CuI·LiBr and with phenylzinc chloride in the presence of catalytic amounts of Pd(PPh₃)₄ is examined. The copper-mediated substitution gives the desired pyridylallenes with good yield only if chelate formation between substrate and cuprate is not possible. In contrast, both chelating and non-chelating propargylic acetates can be converted efficiently into the corresponding pyridyl allenes under palladium catalysis.

allenes - copper - zinc - palladium - pyridines

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