Inversion of Configuration at the Phosphorus Nucleophile in the Diastereoselective and Enantioselective Synthesis of P‐Stereogenic syn‐Phosphiranes from Chiral Epoxides

Nucleophilic substitution results in inversion of configuration at the electrophilic carbon center (SN2) or racemization (SN1). The stereochemistry of the nucleophile is rarely considered, but phosphines, which have a high barrier to pyramidal inversion, attack electrophiles with retention of configuration at P. Surprisingly, cyclization of bifunctional secondary phosphine alkyl tosylates proceeded under mild conditions with inversion of configuration at the nucleophile to yield P‐stereogenic syn‐phosphiranes. DFT studies suggested that the novel stereochemistry results from acid‐promoted tosylate dissociation to yield an intermediate phosphenium‐bridged cation, which undergoes syn‐selective cyclization. Nucleophile Substitution verläuft mit Inversion (SN2) oder Racemisierung (SN1) am Elektrophil, aber was ist mit dem Nucleophil? Reagieren P‐stereogene Phosphane als Nucleophile, wird die Konfiguration am Phosphoratom für gewöhnlich beibehalten. Die erste intramolekulare nucleophile Substitution mit Inversion am Phosphorzentrum ist für die diastereo‐ und enantioselektive Synthese von P‐stereogenen syn‐Phosphiranen von entscheidender Bedeutung.