Configurational Lability at Tetrahedral Phosphorus: syn/anti-Isomerization of a P-Stereogenic Phosphiranium Cation by Intramolecular Epimerization at Phosphorus.

Autor: Tipker RM; 6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755, USA., Muldoon JA; 6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755, USA., Pham DH; 6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755, USA., Varga BR; 6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755, USA., Hughes RP; 6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755, USA., Glueck DS; 6128 Burke Laboratory, Department of Chemistry, Dartmouth College, Hanover, NH, 03755, USA., Balaich GJ; Department of Chemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA, 92093, USA., Rheingold AL; Department of Chemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA, 92093, USA.
Jazyk: angličtina
Zdroj: Angewandte Chemie (International ed. in English) [Angew Chem Int Ed Engl] 2022 Jan 03; Vol. 61 (1), pp. e202110753. Date of Electronic Publication: 2021 Nov 23.
DOI: 10.1002/anie.202110753
Abstrakt: Tetrahedral main-group compounds are normally configurationally stable, but P-epimerization of the chiral phosphiranium cations syn- or anti-[Mes*P(Me)CH 2 CHPh][OTf] (Mes*=2,4,6-(t-Bu) 3 C 6 H 2 ) occurred under mild conditions at 60 °C in CD 2 Cl 2 , resulting in isomerization to give a syn-enriched equilibrium mixture. Ion exchange with excess [NBu 4 ][Δ-TRISPHAT] (Δ-TRISPHAT=Δ-P(o-C 6 Cl 4 O 2 ) 3 ) followed by chromatography on silica removed [NBu 4 ][OTf] and gave mixtures of syn- and anti-[Mes*P(Me)CH 2 CHPh][Δ-TRISPHAT]⋅x[NBu 4 ][Δ-TRISPHAT]. NMR spectroscopy showed that isomerization proceeded with epimerization at P and retention at C. DFT calculations are consistent with a mechanism involving P-C cleavage to yield a hyperconjugation-stabilized carbocation, pyramidal inversion promoted by σ-interaction of the P lone pair with the neighboring β-carbocation, and ring closure with inversion of configuration at P.
(© 2021 Wiley-VCH GmbH.)
Databáze: MEDLINE
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