Chiral Auxiliaries and Chirogenesis

This Reprint Book highlights and overviews the most important and novel aspects of chiral auxiliary and chirogenesis in different natural/physical sciences and in modern technologies. In particular, some newly emerging classes of molecules used for these purposes are described. This book consists of four review articles and one research paper and is of interest for general chemistry readership, including graduate and postgraduate students, and for researchers specializing in the fields of chirality and stereochemistr

Synthese von Buckybowls mittels eines Algorithmus zur Aktivierung von C-FBindungen an Aluminiumoxid

The unique nature of the alumina‐mediated cyclodehydrofluorination gives the opportunity to execute the preprogrammed algorithm of the C−C couplings rationally built into a precursor. Such multi‐assemblies facilitate the construction of the carbon‐skeleton, superseding the conventional step‐by‐step by the one‐pot intramolecular assembly. In this work, the feasibility of the aluminamediated C−F bond activation approach for multi‐assembly is demonstrated on the example of a fundamental bowl‐shaped polycyclic aromatic hydrocarbon (diindenochrysene) through the formation of all “missing” C−C bonds at the last step. Among valuable insights into the reaction mechanism and the design of the precursors, a facile pathway enabling the two‐step synthesis of diindenochrysene was elaborated, in which five C−C bonds form in a single synthetic step. It is shown that the relative positions of fluorine atoms play a crucial role in the outcome of the assembly and that governing the substituent positions enables the design of effective precursor molecules “programmed” for the consecutive C−C bond formations. In general, these findings push the state of the field towards the facile synthesis of sophisticated bowl‐shaped carbon‐based nanostructures through multi‐assembly of fluoroarenes

Synthesis of polycyclic aromatics having unusual molecular architectures via cascade cyclization reactions of enyne -allenes

The C2-C6 Schmittel cyclization reaction of the benzannulated enyne-allenes provides an efficient synthetic pathway for the construction of a variety of polycyclic aromatics. By starting from truxenone, the cascade cyclization reactions furnished several unusual and congested polycyclic compounds. The in situ generated enyne-allenes are key intermediates in these cyclization reactions.;A new synthetic approach to 2,2\u27-disubstituted 1,1\u27-binaphthyls and related compounds was also successfully developed by using the benzannulated enediynes as precursors. These 1,1\u27-binaphthyls derivatives can serve as potential BINOL type ligands. The assembly of the enediynyl precursors from three separate aromatic fragments allows the possibility of placing a variety of functional groups at various positions of the 1,1\u27-binaphthyl system.;A 12-step non-pyrolytic synthetic pathway employing the Schmittel cyclization reactions has been developed, leading to a bowl-shaped polycyclic aromatic hydrocarbon (PAH) having a 54-carbon framework of the surface of C60 . Incorporating of sp3-carbons on the 54-carbon framework facilitates the connection of carbon atoms intramolecularly

Condensation of Fivefold-Symmetric Molecules in Two Dimensions

We report the formation of a two-dimensional glass by solidification of a two-dimensional gas of fivefold-symmetric molecules on a copper surface upon cooling. Direct observation with scanning tunneling microscopy allows a detailed insight into the implications of a symmetry mismatch between molecular geometry and crystal lattice

Sumanenylferrocenes and their solid state self-assembly

The first ferrocene-fused organometallic compounds derived from the buckybowl sumanene (C21H12) are presented. Both compounds, sumanenylferrocene and 1,1′-disumanenylferrocene, have been synthesized by Negishi-type cross- coupling of iodosumanene and were studied crystallographically. Sumanenylferrocenes form unique packing motifs, which are both different from those of their corannulene congeners and sumanene itself

Ab Initio Investigations of Gas Adsorption on Buckybowls

Gas separation processes are prevalent in science and industries to isolate desired or remove undesired gases from mixtures. Of the various methods to perform this separation, surface adsorption has been shown to be a promising avenue due to favorable temperature and pressure limits, high capacity, and chemical tunability. This thesis focuses on using a carbon-based, bowl-like molecule known as a Buckybowl to act as a gas adsorbent. The bowl-like nature of this structure has been shown to have stronger dispersion and electrostatic interactions on the concave side suggesting that it is a potential candidate for gas capture and release systems. In this study, the small gas molecules CH$_4$, CO$_2$, NO, and NO$_2$ are explored computationally as adsorbates on to the Buckybowls corannulene and sumanene as well as the planar structure coronene. It is found that the bowl-up orientation of the Buckybowls, with respect to the adsorbate, has the strongest interaction energy (sumanene CH$_4$, -5.6 kcal/mol) followed by coronene (-2.9 kcal/mol) and then the bowl-down configurations (sumanene CH$_4$, -1.8 kcal/mol). Sumanene was found to have the strongest adsorption energies for these molecules (BU CO$_2$, -6.1 kcal/mol) with binding to corannulene (BU CO$_2$, -4.8 kcal/mol) and coronene (CO$_2$, -3.7 kcal/mol) being weaker. The system studied were also found to exhibit stimulus-induced adsorption/desorption. Specifically, the Buckybowls were found to change selectivity towards specific adsorbates in response to an applied electric field as the interaction energy ordering was altered. Beyond atmospheric molecules, the ability of sumanene to adsorb respiratory irritants was also explored. It was found that for three potent irritants, 2-chlorobenzalmalonitrile, 1,6 hexamethylene diisocyanate, and toluene diisocyanate, the interaction energies are about -14 kcal/mol with attraction largely driven by electrostatic and dispersion effects. No significant energetic barriers due to structural changes were found indicating that sumanene could be a possible gas capture system for these chemical compounds

Development of a Synthetic Pathway Toward a Bowl-Shaped C 27H12 Polycyclic Aromatic Hydrocarbon

Bowl-shaped and basket-shaped polycyclic aromatic hydrocarbons (PAHs) have attracted considerable attention in recent years. They are challenging targets for total synthesis due to the presence of substantial strain energy in the curved structures. A solution-phase synthesis of a bowl-shaped polycyclic aromatic hydrocarbon C27H12 was explored. The use of the casecade radical cyclization reactions of a benzannulated enyne-allene is a key feature of this synthetic pathway. The mild reaction conditions provide efficient and flexible designs for bowl-shaped and basked-shaped PAHs and their precursors. Our proposed synthesis strategy for the bowl-shaped C27H12 involves an initial synthesis of a benzannulated enediynyl propargylic alcohols followed by the cascade cyclization reactions of the resulting enyne-allenes. The use of the palladium-catalyzed intramoleular arylation reactions is proposed as a key step leading to the final products. Specifically, transformation of 1-indanone to a key intermediate, 2-methoxy-2-(2- methoxyethyl)-1-indanone, was extensively investigated, and the conditions for forming 1-(2-ethynylphenyl)-2-(2,6-dichlorophenyl)ethyne via the Sonogashira reaction were established. Condensation between the 1-indanone and the ethyny1 derivatives produced the benzannulated enediynyl propargylic alcohol. Chlorinated P AHs as potential precursors leading to the bowlshpaed Cz1H12 hydrocarbon have been successfully synthesized

Lattice Mismatch Drives Spatial Modulation of Corannulene Tilt on Ag(111)

We investigated the adsorption of corannulene (C20H10) on the Ag(111) surface by experimental and simulated scanning tunneling microscopy (STM), X-ray photoemission (XPS), and near-edge X-ray absorption fine structure (NEXAFS). Structural optimizations of the adsorbed molecules were performed by density functional theory (DFT) and the core excited spectra evaluated within the transition-potential approach. Corannulene is physisorbed in a bowl-up orientation displaying a very high mobility (diffusing) and dynamics (tilting and spinning) at room temperature. At the monolayer saturation coverage, molecules order into a close-compact phase with an average intermolecular spacing of 3c10.5 \ub1 0.3 \uc5. The lattice mismatch drives a long wavelength structural modulation of the molecular rows, which, however, could not be identified with a specific superlattice periodicity. DFT calculations indicate that the structural and spectroscopic properties are intermediate between those predicted for the limiting cases of an on-hexagon geometry (with a 3-fold, 3c8.6 \uc5 unit mesh) and an on-pentagon geometry (with a 4-fold, 3c11.5 \uc5 unit mesh). We suggest that molecules smoothly change their equilibrium configuration along the observed long wavelength modulation of the molecular rows by varying their tilt and azimuth in between the geometric constraints calculated for molecules in the 3-fold and 4-fold phases

Amplification of Chirality at Solid Surfaces

Symmetry-breaking phenomena in two-dimensional crystallization at surfaces are reviewed and the potential impact to chiral amplification in three-dimensional systems in connection with the origin of homochirality in the biomolecular world is discussed. Adsorption of prochiral molecules leads to two-dimensional conglomerates, i.e., on a local scale spontaneously to homochiral crystal structures. Small enantiomeric excess or chiral impurities in this environment install homochirality on a global scale, that is, on the entire surfac