Protonation and Alkylation of Ambident (9-Anthryl)arylmethyl Anions

Article abstract of DOI:10.1021/ja00352a025

We have investigated the protonation of ambident (9-anthryl)arylmethylsodiums (Na-2) and -lithiums (Li-2) (substituent =p-Me, p-Me, H, m-F) with various oxygen and carbon acids in tetrahydrofuran to give a mixture of the anthracene derivatives 3a-d and the 9,10-dihydroanthracenes 4a-d.Product compositions were dramatically influenced by the substituent electronic effects of the carbanions 2 and the acidities of the proton donors.In the protonation with the oxygen proton donors the change of the countercation 2 and the addition of hexamethylphosphoramide also exerted remarkable effects on the 3:4 ratio, whereas these two factors were not important in the case of the carbon acids.This fact would be interpreted as the extent of coordination of oxygen acids to metal cations being important in determining protonation regiochemistry.The reaction of (9-anthryl)arylmethyl anions (2a-d) with a series of aliphatic and benzylic halides gave a mixture of two cross-coupling products, 7 (coupling at C-α) and 8 (coupling at C-10), and/or dimers, 5 C_α-C₁₀ coupling) and 6 (C₁₀-C₁₀ coupling), the composition being influenced by the substituent electronic effects of the carbanions 2 and structure of the alkyl groups of the halides.The leaving group effects also have a significant influence on the product composition.Using dependence (or independence) of the product composition on the electronic effects of the substituent of 2 as a tool to differentiate the reaction mechanisms, we have attempted to rationalize the apparently complicated alkylation of the carbanions 2.