Highly Enantiomerically Enriched Chlorophosphine Boranes: Synthesis and Applications as P-Chirogenic Electrophilic Blocks
journal contributionposted on 02.05.2003, 00:00 by Christophe Bauduin, Dominique Moulin, El Bachir Kaloun, Christophe Darcel, Sylvain Jugé
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.