Synthesis, Resolution, and VCD Analysis of an Enantiopure Diazaoxatricornan Derivative

Abstract

Using simple organic synthetic transformations, a novel diazaoxatricornan derivative, the 12 c-methyl-12-phenyl-8-propyl-12,12 c-dihydro-8 H-4-oxa-8,12-diazadibenzo[ cd, mn]pyrene ( 6a), was prepared. This novel chiral cup-shaped molecule was isolated in racemic form and in excellent yield after the addition of methyl lithium to the BF 4 salt of a novel unsymmetrical diazaoxatriangulenium cation. Compound 6a was found to be stable under classical laboratory conditions-something not obvious considering the extreme stability of the carbenium ion precursor, the electron-rich nature of the core, and the strain induced by the pyramidalization of the central carbon. The enantiomers were readily separated by chiral stationary phase chromatography, and the absolute configuration of (-)-( S)- 6a was determined by a comparison of the experimental and theoretical vibrational circular dichroism (VCD) spectra. This isolation of (-)-( S)- 6a and (+)-( R)- 6a constitutes thus the first report of a nonracemic closed-capped chiral bowl molecule for which the chirality is due to the intrinsic dissymmetry of the central core of the structure only.

Synthesis of Enantiopure C3‐Symmetric Triangular Molecules

“…[18] There is ac lass of chiral hydrocarbons that owe their chirality only to asymmetric distribution of masses of the hydrogen nuclei. Despite 14 having the same distribution of protons and electrons as the achiral hydrocarbon 11,i ti s ac hiral molecule.T he only difference between macrocycles 11 and 14 is the placement of neutrons.T he opposite enantiomer of 14 was also synthesized using the opposite asymmetric catalyst, Rh 2 [(R)-NTTL] 4 . [20] Furthermore,determination of the absolute configuration of D-labeled chiral hydrocarbons is also ac hallenge.T he reactions mentioned above were successfully extended to the synthesis of an enantiopure hydrocarbon, the chirality of which is ascribed to asymmetric distribution of H/D atoms on the benzene rings.Initially,the D 2 -triazole 12,which has two deuterium atoms at the 2-and 6positions,was prepared in seven steps starting from 2,6-D 2 -4methylaniline (94 %Dincorporation, see the Supporting Information).…”

“…[1] However,the number of enantiopure C 3 -symmetric molecules synthesized to date is severely limited [2][3][4][5][6] compared with that of C 2 -symmetric molecules,p robably due to the scarcity of appropriate synthetic approaches,a nd thus chemistry based upon C 3 -symmetric molecules remains underdeveloped. [1] However,the number of enantiopure C 3 -symmetric molecules synthesized to date is severely limited [2][3][4][5][6] compared with that of C 2 -symmetric molecules,p robably due to the scarcity of appropriate synthetic approaches,a nd thus chemistry based upon C 3 -symmetric molecules remains underdeveloped.…”

On the synthesis and optical properties of sulfur‐bridged analogues of triangulenium cations and their precursors

“…At this stage, with unsymmetrically substituted salt [ 9 ][BF 4 ] in hands, we decided to test the feasibility of the addition of an organometallic reagent to the carbocationic center;23–26 the resulting azaoxathiatricornan being most probably another example of a chiral bowl‐shaped molecule 22. MeLi (1.6 equiv.)…”

“…1). 3 Triangulenium ions and their derivatives have been strongly studied because of a large array of biological,4–6 chemical,5–9 photochemical/photophysical,10–18 stereochemical,19–22 structural,23–26 supramolecular,27, 28 and synthetic29 properties.…”

“…5 + is also an interesting platform for the discovery of new reactivity and topology 33–35. Compound 6 + was used as a platform for the preparation of a non‐racemic diazaoxatricornan derivative 22…”