Derivatization of (quinolin-8-yl)phosphinimidic amides via ortho-lithiation revisited

Abstract

The direct ortho-lithiation of N–H containing (quinolin-8-yl)phosphinimidic amides by reaction with 1 equiv. of n-BuLi described by Wang and co-workers has been re-examined. The multinuclear magnetic resonance (¹H, ²H, ⁷Li, ¹³C, ¹⁵N and ³¹P) study of the species formed in the monolithiation of N-(tert-butyl)-P,P-diphenyl-N′-(quinolin-8-yl)phosphinimidic amide 5 with n-BuLi in THF showed that proton abstraction occurred exclusively and quantitatively at the NH. The combination of the NMR results with a DFT study made it possible to describe the structure of the N-lithiated species 9 as a dimer consisting of an eight-membered ring showing two lithium ions triply coordinated to nitrogen atoms corresponding to the deprotonated amine and aminoquinoline moieties of different monomers. The formation of a polymer featuring the same coordination mode couldn't be excluded. In addition, optimized conditions for the efficient derivatization of 5via ortho-lithiation were realised. The reaction of 5 with 2.4 equiv. of t-BuLi in THF in the temperature range of −80 °C to 25 °C for 3 h afforded a N,C_ortho-dilithiated species that was trapped with a series of electrophiles leading to new functionalized ortho derivatives of 5 in good yields.