Planar chiral molecular structures

Recent Advances of Chiral Isolated and Small Organic Molecules: Structure and Properties for Circularly Polarized Luminescence

This paper explores recent advancements in the field of circularly polarized luminescence (CPL) exhibited by small and isolated organic molecules. The development and application of small CPL molecule are systematically reviewed through eight different chiral skeleton sections. Investigating the intricate interplay between molecular structure and CPL properties, the paper aims at providing and enlighting novel strategies for CPL-based applications.

Synthesis, stereochemical assignment, and enantioselective catalytic activity of late transition metal planar chiral complexes

Planar chirality is an important form of molecular chirality that can be utilized to induce enantioselectivity when incorporated into transition metal catalysts. However, due to synthetic constraints, the use of late transition metal planar chiral complexes to conduct enantioselective transformations has been limited. Additionally, the published methods surrounding the stereochemical assignment of planar chiral compounds are sometimes conflicting, making proper assignment difficult. This review aims to provide clarity on the methods available to assign planar chirality and provide an overview on the synthesis and use of late transition metal planar chiral complexes as enantioselective catalysts.

Properties of Configurationally Stable Atropoenantiomers in Macrocyclic Natural Products and the Chrysophaentin Family

development of antibiotics, antineoplastics, and therapeutics for other diseases. Natural products are unique among all other small molecules in that they are produced by dedicated enzymatic assembly lines that are the protein products of biosynthetic gene clusters. As the products of chiral macromolecules, natural products have distinct three-dimensional shapes and stereochemistry is often encoded in their structures through the presence of stereocenters, or in the case of molecules that lack a stereocenter, the presence of an axis or plane of chirality. In the latter forms of chirality, if the barrier to rotation about the chiral axis or chiral plane is sufficiently high, stable conformers may exist allowing for isolation of discrete conformers, also known as atropisomers. Importantly, the diverse functions and biological activities of natural products are contingent upon their structures, stereochemistry and molecular shape. With continued innovation in methods for natural products discovery, synthetic chemistry, and analytical and computational tools, new insights into atropisomerism in natural products and related scaffolds are being made. As molecular complexity increases, more than one form of stereoisomerism may exist in a single compound (for example, point chirality, chiral axes, and chiral planes), sometimes creating atypical or noncanonical atropisomers, a term used to distinguish physically noninterconvertable atropisomers from typical atropisomers.Here we provide an account of the discovery and unusual structural and stereochemical features of the chrysophaentins, algal derived inhibitors of the bacterial cytoskeletal protein FtsZ and its associated protein partners. Eleven members of the chrysophaentin family have been discovered to date; seven of these are macrocyclic bis-bibenzyl ethers wherein the site of the ether linkage yields either a symmetrical or asymmetrical macrocyclic ring system. The asymmetrical ring system is highly strained and corresponds to the compounds having the most potent antimicrobial activity among the family. We review the structure elucidation and NMR properties that indicate restricted rotation between axes of two biaryl ethers, and the plane represented by the substituted 2-Z-butene bridge common to all of the macrocycles. Computational studies that corroborate high barriers to rotation about one representative plane, on the order of 20+ kcal/mol are presented. These barriers to rotation fix the conformation of the macrocycle into a bowl-like structure and suggest that an atropisomer should exist. Experimental evidence for atropisomerism is presented, consistent with computational predictions. These properties are discussed in the context of the total synthesis of 9-dechlorochrysophaenin A and its ring C isomers. Last, we discuss the implications for the presence of enantiomers in the biological activity and macrocyclization of the natural product.

Am1 study of Conformational properties of (E)-Cyclononene

The unsymmetrical chair–chair (CC) conformation of (E)-cyclononene is calculated to be 5.7 kJ/mol more stable than the axial-symmetrical twist-chair-chair (TCC) form; the calculated energy barrier for ring inversion of the CC conformation is 45.6 kJ/mol, while the barrier for swivelling of the double bond through the polyethylene bridge is 119.5 kJ/mol.

Control of a Chiral Property of a Calix[3]aramide: The Racemization Suppressed by Intramolecular Cyclic Hydrogen Bonds and DMSO-H2O System-Induced Spontaneous Resolution

A calix[3]aramide has been synthesized bearing three triphenylphosphinic amide moieties, which formed intramolecular cyclic hydrogen bonds that suppressed its cone/partial cone inversion. The intramolecular cyclic hydrogen bonds were disrupted by DMSO, and the insertion of H2O into the hydrogen bonds triggered the spontaneous resolution of the calix[3]aramide. Within a chiral environment, such as that afforded by the presence of optically active 2-butanol, the calix[3]aramide underwent a symmetry breaking crystallization process.

Use of mixed Li/K metal TMP amide (LiNK chemistry) for the synthesis of [2.2]metacyclophanes

A new two-step general approach to [2.2]metacyclophane synthesis from substituted m-xylenes is described. The strategy employs a selective benzylic metalation and oxidative C-C bond formation for both synthetic operations. Regioselective benzylic metalation is achieved using the BuLi, KOt-Bu, TMP(H) (2,2,6,6-tetramethylpiperidine) combination (LiNK metalation conditions) and oxidative coupling with 1,2-dibromoethane. The synthetic ease of this approach compares favourably with previously reported methods and allows for ready access to potentially useful planar chiral derivatives.

The synthesis and conformation of oxygenated trianglimine macrocycles

The synthesis of series of D(2h) and C(2v) symmetric oxygenated aromatic dicarboxaldehydes, using dilithiation methodology, is described along with their reactivity in the [3+3] cyclocondensation reaction with (1R,2R)-diaminocyclohexane to give oxygenated trianglimine macrocycles. Macrocycles derived from C(2v) symmetric dialdehydes give macrocycles with a stereogenic aromatic plane with complete diastereocontrol, as a mixture of rotamers.

Planar chirality: cycloaddition and transannular reactions of optically active azoninones that contain (E)-olefins

Unsaturated nine-membered ring lactams that contain (E)-olefins within the ring are characterized by planar chiral properties. Thus, selective conversions of the double bond allowed a complete transfer of the planar chiral information into new stereogenic centers The basis of the transformations was the high activation barrier that prevented efficient flipping of the double bond at room temperature (epimerization pR <=> pS) with respect to the ring. Cycloadditions led diastereoselectively to cyclopropano, epimino, epoxy, and dihydroxy azonanones under mild conditions with moderately high yields. The epoxy azonanones were subjected to regio- and diastereoselective transannular epoxide opening/ring contraction sequences to give hydroxy indolizidinones. The regiochemical and stereochemical outcome strongly depends on the configuration of the oxirane and the chiral information of the lactam unit. The so-formed optically active bicycles with defined substitution patterns should serve as versatile building blocks in alkaloid synthesis.