Highly Enantiomerically Enriched Chlorophosphine Boranes:  Synthesis and Applications as P-Chirogenic Electrophilic Blocks

Abstract

The stereoselective synthesis of P-chirogenic chlorophosphine boranes 4 was investigated by HCl acidolysis of the corresponding aminophosphine boranes 10. The reaction afforded the P-N bond cleavage with inversion of the configuration at the phosphorus center, leading to the chlorophosphine boranes 4 with high to excellent enantiomeric purities (80-99% ee), except in the case of the chloro-1-naphthylphenylphosphine borane 4d. Reaction conditions and workup significantly influence the enantiomeric purity of the product, with the exception of the o-anisyl- and o-tolylchlorophenylphosphine boranes, 4b and 4c, which were found to be particularly stable even after purification by chromatography on silica gel. Reaction of the chlorophosphine boranes 4 with various nucleophiles, such as carbanions, phenolates, thiophenolates, or amides, afforded the corresponding organophosphorus borane complexes via P-C, P-O, P-S, and P-N bond formation, respectively, in 34-93% yield and with up to 99% ee. This work demonstrates the importance of chlorophosphine boranes 4 as new and powerful electrophilic building blocks for the highly stereoselective synthesis of P-chirogenic organophosphorus compounds.

Modular P‐Chirogenic Aminophosphane‐Phosphinite Ligands for Rh‐Catalyzed Asymmetric Hydrogenation: A New Model for Prediction of Enantioselectivity

“…The free AMPP 4a-l ligands were readily purified by filtration through neutral alumina, and their diastereomeric purities were checked by 31 P NMR spectroscopy. When the ring-opened products 6 are treated with a Pchirogenic chlorophosphane borane 8 [60] and then decomplexed with DABCO, the corresponding AMPP ligands 4m-p, featuring additional chirality at the phosphinite fragment, are obtained (Scheme 3, b; Table 1, Entries 13-16). Interestingly, the epimeric P-chirogenic AMPP ligands 4n and 4o are obtained by use of the two enantiomers of the o-anisylchlorophenylphosphane borane 8, which are also prepared independently from (+)-or (-)-ephedrine (Table 1, Entries 14,15).…”

“…In addition, the AMPP 4Јq (R 1 ,R 2 = o-An; R 3 = Ph), featuring both P-chirogenic aminophosphane and phosphinite residues, was obtained by the same methodology, but starting from (-)-ephedrine, followed by the trapping of the ring-opened intermediate 6Ј with the (S)-o-anisylchlorophenylphosphane borane 8 [56,60] (Table 1, Entry 17).…”

Preparation of phosphines through C–P bond formation

“…Acidolysis with HCl of compounds 8a results in the stereoselective synthesis of chiral chlorophosphine boranes 11a [39]. The borane complex has a good configurational stability with borane as a protecting group, in contrast to chlorophosphines that can undergo inversion at the phosphorus center [30].…”

Cyclic tri- and Pentavalent Amidoesters and Diamides with a Stereogenic Phosphorus Atom in Asymmetric Synthesis: Part I: Stoichiometric Reagents

“…It is interesting to note that the o-anisyl-and otolylchlorophenylphosphine boranes were found to be particularly stable even during purification by chromatography on silica gel. Reaction of the chlorophosphine boranes 24 with various nucleophiles, such as carbanions, phenolates, thiophenolates, or amides, afforded the corresponding organophosphorus borane complexes 25 via P-C, P-O, P-S, and P-N bond formation, respectively, in 34-93% yield and with up to 99% ee (Scheme 8) [31]. Soon after publication of the first report, this methodology was adopted worldwide [32][33][34][35][36][37][38][39] and very recently several 2,6-disubstituted aryl groups were successfully appended to the phosphorus atom, giving the corresponding, sterically congested (N-ephedrino)phosphine boranes 20a with dr 99:1 [40].…”