Abstract
The intramolecular oxy-carbonylation of terminal acetylenes is considered to be a useful method for the conversion of an acetylene unit to a β-ketoester unit utilizing neighboring group participation. The first examples of an asymmetric version of this reaction have been achieved, using some new chiral bis-oxazoline (box) ligands. To demonstrate the utility of this reaction, the chiral total synthesis of (+)-bakkenolide-A was achieved. The box ligand plays an important role in the intramolecular oxy-carbonylation of propargyl acetate having an extra terminal acetylene. In the absence of the box ligand, the second triple bond did not react, affording a cyclic orthoester. The use of the box ligand changed the course of the reaction significantly, yielding either 4-cyclopentene-1,3-dione or a bicyclic lactone by tandem carbonylative cyclization as a result of the reaction (insertion or methoxy-palladation) of the second triple bond.
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