Metal-Ammonia Ring Reduction of Aromatic Carboxylic Acid Esters

Article abstract of DOI:10.1021/jo00183a014

Although esters are often reduced to alcohols with metal-ammonia solutions, it has been found that aromatic carbocyclic acid esters can be reduced efficiently to the corresponding dihydro aromatics when 1.25 equiv of water is present before metal addition.The general effect of the presence of water (before metal addition) upon metal-ammonia reduction of polycyclics was tested with anthracene (0.5g), which was reduced to 9,10-dihydroanthracene (97percent yield) in the presence of 3.5g of water.Polynuclear aromatic esters are reduced smoothly by this technique, but in the absence of water, alkyl 9-anthroates gave a dimer assigned as axial/axial on the basis of nuclear Overhauser enhancements.Possible mechanistic pathways for dimer formation were investigated by the addition of 9,10-dihydroanthracene monoanion as well as anthracene dianion to ammonia/THF solutions of ethyl anthroate.This led to dimer and trimer formation, respectively.The structures of these compounds are discussed in light of their carbon and proton NMR spectra.