The Replacement of Electronegative Substituents by an Electron-transfer Mechanism. The Factors Governing the Reaction of Carbonyl and Imino Compounds with Organomagnesium Reagents

Abstract

Abstract For the purpose of studying the electron-transfer initiated replacement of ortho-methoxy and ortho-halogeno substituents of diaryl ketone anils by the aryl group of ArMgBr, eight anils were prepared. The expected o-methoxy replacement by the phenyl group of PhMgBr, however, was extremely slow, and no o-chloro replacement took place. In contrast, anils of 1-substituted (MeO, Br, Cl) fluorenones gave the replacement products: The distribution of by-products formed via radical pathway in the cases of halogeno-anils was clearly different from that in the case of the methoxy-anil. In the reaction with ArN(MgBr)2, 1-halogenofluorenones afforded the normal condensation products, while 1-methoxyfluorenone gave the “condensation-replacement” product. On the basis of the characteristic product-distributions obtained in the two organomagnesium reactions, the mechanism of methoxy replacement was distinguished from that of halogen replacement. Factors governing the two reactions were proposed and discussed: The structures of the substrates favorable to spin-delocalization, the electron-accepting ability of the substrates, the electron-donating ability of the reagents, the leaving ability of substituents, and their leaving manner.