Metal ions and complexes in organic reactions. Part XX. Copper-catalysed reactions of aromatic bromo-carboxylates with carbanions, giving oxo-acids, isocoumarins, and related products

Abstract

Depending upon choice of solvent and other conditions, copper-catalysed reactions of sodium o-bromobenzoate with sodium acetylacetonate gave o-(diacetylmethyl)benzoic acid (1), o-acetonylbenzoic acid (2), or 3-methylisocoumarin (3), whereas reactions with ethyl sodioacetoacetate gave compound (2) or (3) or o-(ethoxycarbonylmethyl)benzoic acid (5); analogously, the products o-CO₂H·C₆H₄·CH(CO₂Et)₂[or (5)], o-CO₂H·C₆H₄·CH(CN)·CO₂H, and o-CO₂H·C₆H₄·CH(CN)₂ were obtained with the corresponding nucleophiles. Sodium 1-bromo-2-, 3-bromo-2-, and 8-bromo-1-naphthoate gave similar substitution products, including, in the first two cases, naphthopyranones. Nucleophilic substitution by the carbanions was ineffective with substrates not containing a carboxylate-salt group adjacent to the halogen. Reductive substitution of halogen competed to a varying extent. Copper could be introduced as metal, or Cu^I or Cu^II species, but the effective reaction intermediates are considered to be copper(II) complexes incorporating the halogeno-carboxylate substrate and the carbanionic nucleophile.