Rock around the Ring: An Experimental and Theoretical Study of the Molecular Dynamics of Stannyltriphospholes with Chiral Tin Substituents

Abstract

The reaction of diphenyltin dichloride with enantiopure Grignard reagents prepared in situ leads to diphenyltin chlorides 7a-e, which contain chiral organyl substituents. The 2-bornyl derivative 7a forms a mixture of exo and endo isomers and the (-)-menthyl derivative 7b yields a mixture of epimers, whereas the cis-and trans-myrtanyl complexes 7c and 7d and the m-(2-bornyl-2-ene)phenyl species 7e form only one enantiomer as the tin atom is separated from the next stereogenic centre by a methylene or m-phenylene group. The target chirally modified 1-(triorganylstannyl)-1,2,4-triphospholes 2a-e are accessible from 7a-e by treatment of the latter with the salt (3,5-di-tert-butyl-1,2,4-triphospholyl)-sodium (Na5) in good yield. As for 7c-e, complexes 2c-e exhibit enantiopure organyl tin substituents that combine with the planar chiral 1,2,4-triphosphole moiety to form diastereomers. X-ray diffraction studies on crystalline phases of

Cage Chirality of PC Cage Compounds: Highly Diastereoselective Formation of Diastereomeric P5‐Deltacyclenes, Separation of Diastereomers, and Removal of the Chiral Auxiliary

“…The stereochemistry of the trans-myrtanyl moiety is the same as that of the starting material 6 b. [7] The two enantiomeric cage units of 7 b represent the same stereoisomers that were identified to form the enantiomers of SnPh 3 -substituted cage model compound 3. [5] No change in the connectivity of related nuclei was observed, and no remarkable changes in the cage bonding distances or angles took place ( Table 2).…”

“…Due to the lack of suitable chromophores, the CD curves of starting materials (À)-cismyrtanol and (À)-cis-myrtanyldiphenylstannyl chloride [7] exhibit only weak Cotton effects, which are only observable in amplified spectra. The same observation can be made with the mixture of diastereomers 7 a-A C H T U N G T R E N N U N G (RR+SR), which is strong evidence for an almost perfect 1:1 mixture, eliminating the chiroptical influence of the two enantiomeric cage units.…”

“…A regular byproduct in small amounts was a known P 6 -A C H T U N G T R E N N U N G (tBuC) 4 H 2 cage, [11] which was introduced most probably into the reaction mixtures together with the starting triphos-A C H T U N G T R E N N U N G pholes. [7] Repeated attempts to separate the diastereomers of 7 b and 7 c by fractional crystallization in several solvents failed, but were successful for the cis-myrtanyl compound 7 a. Carefully concentrated solutions of 7 a in n-hexane at 4 8C (one week) led to the crystallization of small amounts of pure 7 a(RR) in crystallographic quality.…”

“…In a previous paper, we reported on the preparation of three diastereomeric derivatives (6 a-c) of stannyl triphosphole 2 with chiral groups R* attached to the tin atom [7] (Scheme 2). Due to the highly dynamic stannyl groups, the saturated ring phosphorus atoms of 6 a-c represent labile stereogenic centers in rapid epimerization equilibrium, but the chosen chiral auxiliary groups are stereochemically inert.…”

“…1: reference [17]; 6 ac: reference [7]. NMR solvents, solvents for chemical reactions and chromatography, and static phases were purchased from standard commercial resources.…”