Asymmetric synthesis of P-stereogenic o-hydroxyaryl-phosphine (borane) and phosphine-phosphinite ligands

Modular Synthesis of Chiral Phosphine‐Phosphite‐Ligands from Phenolic Precursors: A New Approach to Bidentate Chelate Ligands Exploiting a PO to PC Migration Rearrangement

“…In such a process, an ortho-lithiated and borane-protected aryl phosphinite (11) would be supposed to rearrange to a more stable ortho-phosphanylphenolate of type 12 [13] from which the intermediates of type 8 would be obtained after work-up in a still borane-protected (thus easier to handle) form.…”

“…It is worthy of note that n-BuLi (even at 0 8C) could be used instead of t-BuLi at À78 8C (as described in the original protocol). [13] Moreover, even if the starting material (14) was contaminated to some extent with the dibrominated species, the reaction product (15) was obtained in very pure form, as a result of a process of "self-purification" under the reaction conditions (due to non-productive Br/Li exchange followed by protonation during work-up). Both the borane-protected phosphinites (14) and the corresponding rearranged phosphines (15) proved to be air-stable and, in most cases, nicely crystalline compounds.…”

“…Inspired by the work of Heinicke [12] and, in particular, JugØ, [13] we envisioned exploiting a P À O to P À C migration rearrangement to introduce the phosphanyl substituent in the ortho-position without the requirement to protect the phenol functionality (Scheme 2). In such a process, an ortho-lithiated and borane-protected aryl phosphinite (11) would be supposed to rearrange to a more stable ortho-phosphanylphenolate of type 12 [13] from which the intermediates of type 8 would be obtained after work-up in a still borane-protected (thus easier to handle) form.…”

Diastereoselective Synthesis of New P‐Stereogenic (ortho‐Hydroxyaryl)diazaphospholidine–Borane Complexes by a Totally Stereoselective P–O to P–C Migration Rearrangement

“…[19] In this context, Jugé et al reported a stereoselective synthesis of P-stereogenic 2-hydroxyarylphosphane ligands, using the borane complexation methodology (Scheme 3). [20] Scheme 1. Totally diastereoselective synthesis of (ortho-hydroxyaryl)diazaphospholidine-borane complexes.…”

“…Intramolecular ortho-Fries-like rearrangement of enantio-enriched ortho-bromoaryl phosphinite-borane complexes. [20] In this paper, we wish to report a totally diastereoselective synthesis of new P-stereogenic (o-hydroxyaryl)diazaphospholidine-borane complexes, based on an intramolecular ortho-Fries-like rearrangement of diastereomerically pure (ortho-bromoaryloxy)diazaphospholidine-borane complexes. The X-ray diffraction of the structures of one product and its precursor shows unambiguously the stereoselectivity of the P-O to P-C rearrangement at the phosphorus atom.…”