Organolithiums by reductive lithiation: the catalytic aromatic method versus the use of preformed aromatic radical-anions. Naphthalene can behave as a catalyst or an inhibitor

Two common modes, using aromatic radical-anions for reductive lithiation, the replacement of a C-heteroatom bond with a C-Li bond, have been compared with regard to yield and the mildness of reaction conditions required. It was found that the use of preformed radical-anions generally resulted in higher yields and milder reaction conditions than the ‘catalytic’ method in which catalytic amounts of the aromatic compound are used and the radical-anion is generated and used in situ. The one apparent exception is N-phenylaziridine, but it is shown that in this case the aromatic compound, naphthalene, is actually an inhibitor rather than a catalyst. Rational mechanistic explanations are given.