Chirality in the Absence of Rigid Stereogenic Elements: Steric and Electronic Effects on the Configurational Stability of C3 Symmetric Residual Tris‐Aryl Phosphanes. Issue 10 (7th March 2014)

• Record Type: Journal Article
• Authors: Rizzo, Simona; Cirilli, Roberto; Pierini, Marco
• Is Part Of: Chirality. Volume 26:Issue 10(2014:Oct.)
• Page Start: 601
• Page End: 606
• Publication Date: 2014-03-07
• Subjects: Chirality -- Periodicals; Pharmaceutical chemistry -- Periodicals; 541.22
• DOI: 10.1002/chir.22292
• Languages: English
• ISSNs: 0899-0042

Abstract

<abstract abstract-type="main"> <title>ABSTRACT</title> <p> <italic>Residual</italic> stereoisomers result whenever closed subsets of appropriately substituted interconverting isomers (the <italic>residual</italic> stereoisomers) are generated from a full set of stereoisomers under the operation of a favored stereomerization mechanism. In the case of the three‐bladed propellers, differentiation of the edges of the blades and strict correlation in the motion of the rings are the prerequisites for the existence of <italic>residual</italic> stereoisomers. In these systems, the two‐ring flip mechanism is the lowest energy process. It does not interconvert all possible conformational stereoisomers generated by helicity and the three‐blade‐hub rotors. In the case of <italic>C</italic><sub>3</sub> symmetric systems, two noninterconverting subgroups (the <italic>residual</italic> stereoisomers) are generated, each one constituted of quickly interconverting diastereoisomers. A series of tris‐aryl phosphanes, structurally designed for existing as <italic>residual</italic> enantiomers or diastereoisomers, bearing substituents differing in size and electronic properties on the aryl rings, were synthesized and characterized. The configurational stability of <italic>residual</italic> phosphanes, evaluated by dynamic <sup>1</sup>H‐ and <sup>31</sup>P‐NMR analysis and by dynamic <named-content content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">enantioselective</named-content> high‐performance <named-content content-type="chemicalTechnology" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">liquid chromatography</named-content> (HPLC), was found 10 kcal mol<sup>‐1</sup> lower than that shown by the corresponding phosphane‐oxides. In accordance with the calculations, an unexpectedly low barrier for phosphorus pyramidal <named-content content-type="reactionType" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">inversion</named-content> was invoked as responsible for the scarce configurational stability of the <italic>residual</italic> tris‐arylphosphanes. <italic>Chirality 26:601–606, 2014</italic>. © 2014 Wiley Periodicals, Inc.</p> </abstract>