Magnesium Adducts of Substituted Anthracenes – Preparation and Properties

2-Methyl-, 1,4-dimethyl-, 9-methyl-, 9-ethyl-, 9,10-dimethyl-, and 9-phenylanthracene (1a–f) react with magnesium in THF at room temperature to afford the corresponding substituted magnesium anthracenes 2a-i. 9,10-Diphenylanthracene (1g), however, reacts with magnesium under the same conditions to produce the deep-blue magnesium bis(9,10-diphenylanthracenide) · 6 THF (4g). Upon heating to 60°C in THF, 4g reversibly dissociated to give magnesium 9,10-diphenylanthracene · 3 THF (2g) and 1g, while prolonged heating at 60°C causes decomposition of 2g to active magnesium (Mg*) and 1g. In THF 2a–c, e, and f exhibit temperature-dependent equilibria with 1a–c, e, and f and magnesium. Compared with magnesium anthracene · 3 THF (2), these equilibria are strongly shifted toward substituted anthracenes and magnesium, and only at 0°C high conversions are achieved. The magnesium exchange between 2 and the substituted anthracenes 1a,b, and f in THF has been experimentally verified. 2a,e, and f react with organic halides in the same way as 2, however, in the case of allyl, propargyl, and benzyl chloride the yields of Grignard compounds are lower than for 2; with bromobenzene, the tendency for the radical transfer reaction is stronger than for 2. Magnesium 9,10-dimethylanthracene (2e) reacts with ethyl acetate to give the bicyclic tertiary alcohol 9 by an intramolecular C–C coupling reaction.