Propargyl Methyl Ethers: Novel Precursors to Cobalt-Complexed Propargyl Cations

Overview

Objectives/Goals The generation of transition metal-stabilized organic cations under neutral conditions has long been sought after in the field of organometallic chemistry. Traditionally, unsaturated organic ligands are treated with strong Lewis acids, such as tetrafluoroboric acid (HBF4). This method, however, is inapplicable for substrates containing functional groups sensitive to acids, in particular benzyloxy and acetal groups. Methods/Materials The novel method for the generation of Co2(CO)6-complexed propargyl cations under neutral conditions was developed: employing the metal-bonded methyl propargyl ethers as substrates and triflic anhydride as a reagent. Results Ionic propargyl triflates are formed in situ as intermediates, due to successive nucleophilic substitution reactions. The transition of these reactive intermediates to the respective propargyl radicals readily occurs at 83°C (3-6 min), by way of the cluster-to-cluster and cluster-to-ligand single electron transfers. The carbon-carbon formation alpha to the metal clusters affords polysubstituted 3,4-diaryl-1,5-alkadiynes in high yields (>80%) and excellent d,l-diastereoselectivity (89-97%). Conclusions/Discussion The scope of the reaction was expanded by involving topologically diverse propargyl ethers, particularly those containing methoxy groups on the periphery of the aromatic nuclei.

Competition history

• CSEF 2010 Chemistry · Entry S0513

Resources

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