| Abstract
| - The mechanism of the anionic cyclization dearomatizing reaction of N-benzyl-N-methyldiphenylphosphinamide (1) upon treatment with s-BuLi in tetrahydrofuran (THF) at −90 °C has been analyzed bydeuterium-labeling and natural abundance multinuclear magnetic resonance (1H, 2H, 7Li, 13C, 31P) studies.In the absence of coordinating cosolvents such as hexamethylphosphoramide (HMPA), eight major anionicspecies were identified, which allowed us to unravel the pathway of the metalation reaction. In agreementwith the complex-induced proximity effect (CIPE) mechanism, the sequence of transformations emergingfrom this study involves the coordination of the lithium base to the PO group of 1 to give four dimericprecomplexes whose NMR data are consistent with structures Va/Vb and VIIIa/VIIIb. The diastereomersVa/Vb are the precursors of the monomeric benzylic anion II, whereas the VIIIa/VIIIb diastereomers areassumed to undergo ortho deprotonation leading to anions I. Translocation from the ortho anion to thebenzylic one is not observed. Intramolecular conjugate addition of anion II to the P-phenyl rings happensin a reversible way, affording the monomeric dearomatized anions III, IV, VI, and VII. The reaction progressesto yield a mixture containing only the species I, III, and IV. HMPA acts as a catalyst for the ortho-to-benzylic translocation and anionic cyclization reactions. Two-dimensional (2D) 7Li,31P{1H} shift correlationsand 7Li{31P} NMR spectra proved to be crucial for the structural assignment of the anionic species. Thesetechniques also demonstrated the diastereotopicity of the two achiral ligands involved in a dimer with s-BuLi(Vb) owing to the slow configuration inversion of the carbanion center.
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