title: Diastereoselective Ortho Lithiation of Phosphinimidic Amides: A Multinuclear Magnetic Resonance and Computational Study.
abstract: The structure of the dianion (SP,RC)-10 formed in the diastereoselective N,Corthodilithiation of the phosphinimidic amide (RC)-Ph2P(═NCO2Me)NHCH(Me)Ph (5; dr of 95:5) with tert-butyllithium in THF has been elucidated using multinuclear magnetic resonance methods, including 2D7Li,nX-HMQC (nX =15N,31P) correlations. (SP,RC)-10 consists of a monomer in which C,N and N,O chelation of the lithium cations generates a system containing a five- and a six-membered metallacycle, respectively, sharing a P-N bond with the lithium atoms connected through the NCO moiety of the phosphazenyl group. Selective deprotonation of the pro-S P-phenyl ring of 5 was ascertained through NOE measurements. DFT computations at the M06-2X(SMD,THF)/6-311+G(d,p)//M06-2X/6-31G(d) level showed that the stereoselective ortho deprotonation process fulfills the features of the CIPE model. The P═N linkage of the N-lithiated species (RC)-8 acts as a directing metalation group via N···LitBu coordination. The mixed complex that is formed evolves to a more stabilized species due to the intramolecular coordination of the OMe group to the lithium cation of the base. Abstraction of the ortho proton proceeds with energy barriers of 12.4 and 13.3 kcal/mol for the pro-R and pro-S phenyl rings. The preference for the latter is explained in terms of the Curtin-Hammett principle.
authors.affiliation: Área de Química Orgánica, Universidad de Almería , Carretera de Sacramento s/n, 04120 Almería, Spain.
authors.forename: Fernando
authors.initials: F
authors.lastname: López Ortiz
authors.affiliation: Área de Química Orgánica, Universidad de Almería , Carretera de Sacramento s/n, 04120 Almería, Spain.
authors.forename: Jesús
authors.initials: J
authors.lastname: García López
authors.affiliation: Área de Química Orgánica, Universidad de Almería , Carretera de Sacramento s/n, 04120 Almería, Spain.
authors.forename: María
authors.initials: M
authors.lastname: Casimiro
authors.affiliation: Área de Química Orgánica, Universidad de Almería , Carretera de Sacramento s/n, 04120 Almería, Spain.
authors.forename: María José
authors.initials: MJ
authors.lastname: Iglesias