meso‐Cumulenic 2H‐Corroles from meso‐Ethynyl‐3H‐corroles

Alkynyl‐substituted 3H‐corrole 9 a was converted to [3]cumulenic 2H‐corrole 10 a by treatment with trimethylsilyl chloride (TMSCl), and 1,3‐butadiyne‐bridged 3H‐corrole dimer 11 b was transformed into [5]cumulene‐bridged 2H‐corrole dimer 12 b by oxidation with PbO₂. Both 10 a and 12 b were metalated to form Zn^II complexes 10 a‐Zn and 12 b‐Zn . The structures of 10 a‐Zn and 12 b‐Zn show planar conformations with bond‐length alternations that are analogous to those of tetraaryl [n]cumulenes. The cumulenic corrole dimers 12 b and 12 b‐Zn display large NIR absorption bands in the range of 700–1400 nm (maximum ϵ≈1.0×10⁵ m ⁻¹ cm⁻¹) owing to the effective π‐conjugation between the two corrole units through the [5]cumulene bridge.     

Asymmetric Strecker Reaction Arising from the Molecular Orientation of an Achiral Imine at the Single‐Crystal Face: Enantioenriched l‐ and d‐Amino Acids

Strecker synthesis has long been considered one of the prebiotic reactions for the synthesis of α‐amino acids. However, the correlation between the origin of chirality and highly enantioenriched α‐amino acids through this method remains a puzzle. In the reaction, it may be conceivable that the handedness of amino acids has been determined at the formation stage of the chiral intermediate α‐aminonitrile, that is, the enantioselective addition of hydrogen cyanide to an imine. Herein, an enantiotopic crystal surface of an achiral imine acted as an origin of chirality for the enantioselective formation of α‐aminonitriles by the addition of HCN. In conjunction with the amplification of the enantiomeric excess and multiplication of enantioenriched aminonitrile, a large amount of near enantiopure α‐amino acids, with the l ‐ and d ‐handedness corresponding to the molecular orientation of the imine, is reported.     

Stereospecific α‐Sialylation by Site‐Selective Fluorination

Sialic acids are ubiquitous components of mammalian cell membranes and key regulators of cellular recognition events. Located at the non‐reducing termini of bioactive gangliosides, these essential building blocks are fused to the polysaccharide core via a characteristic α‐linkage, and rarely occur in the monomeric form. Effective chemical strategies to enable α‐sialylation are urgently required to construct well‐defined tools for glycomics. To complement existing chemoenzymatic strategies, an α‐selective process has been devised based on the site‐selective introduction of fluorine at C3 (more than 20 examples, up to 90 % yield). Predicated on localized particle charge inversion (C?H^δ+→C?F^δ?), fluorine insertion simultaneously augments the anomeric effect, enhances electrophilicity at C2 and mitigates elimination. A stereochemical induction model is postulated that spans the S_N continuum and validates the role of the C?F bond in orchestrating α‐selectivity.     

Diferrocenophosphaborin: A Planar‐Chiral,Redox‐Active and Anion‐Responsive Ambiphilic Ligand

A new class of Janus‐like ambiphilic ligands is introduced. The rigid diferrocene backbone in heterocycles 4‐SnP and 4‐BP creates an unprecedented chiral environment as demonstrated by multinuclear NMR and single‐crystal X‐ray studies. In addition, the ligands are redox‐responsive and the Lewis acidic borane moiety in 4‐BP can be exploited to further tune the properties: a clear decrease in the CO stretching frequency of a Vaska‐type Rh^I complex 5‐BP is observed upon addition of fluoride ions. Thus, the Lewis acid and Lewis base sites influence each other and their strength can be modulated by redox chemistry and anion binding.     

Regio‐ and Enantio‐selective Chemo‐enzymatic C−H‐Lactonization of Decanoic Acid to (S)‐δ‐Decalactone

The conversion of saturated fatty acids to high value chiral hydroxy‐acids and lactones poses a number of synthetic challenges: the activation of unreactive C?H bonds and the need for regio‐ and stereoselectivity. Here the first example of a wild‐type cytochrome P450 monooxygenase (CYP116B46 from Tepidiphilus thermophilus) capable of enantio‐ and regioselective C5 hydroxylation of decanoic acid 1 to (S)‐5‐hydroxydecanoic acid 2 is reported. Subsequent lactonization yields (S)‐δ‐decalactone 3 , a high value fragrance compound, with greater than 90 % ee. Docking studies provide a rationale for the high regio‐ and enantioselectivity of the reaction.     

On‐Surface Evolution of meso‐Isomerism in Two‐Dimensional Supramolecular Assemblies

Chiral structures created through the adsorption of molecules onto achiral surfaces play pivotal roles in many fields of science and engineering. Here, we present a systematic study of a novel chiral phenomenon on a surface in terms of organizational chirality, that is, meso‐isomerism, through coverage‐driven hierarchical polymorphic transitions of supramolecular assemblies of highly symmetric π‐conjugated molecules. Four coverage‐dependent phases of dehydrobenzo[12]annulene were uniformly fabricated on Ag(111), exhibiting unique chiral characteristics from the single‐molecule level to two‐dimensional supramolecular assemblies. All coverage‐driven phase transitions stem from adsorption‐induced pseudo‐diastereomerism, and our observation of a lemniscate‐type (∞) supramolecular configuration clearly reveals a drastic chiral phase transition from an enantiomeric chiral domain to a meso‐isomeric achiral domain. These findings provide new insights into controlling two‐dimensional chiral architectures on surfaces.     

Near‐Infrared Free‐Radical and Free‐Radical‐Promoted Cationic Photopolymerizations by In‐Source Lighting Using Upconverting Glass

A method is presented for the initiation of free‐radical and free‐radical‐promoted cationic photopolymerizations by in‐source lighting in the near‐infrared (NIR) region using upconverting glass (UCG). This approach utilizes laser irradiation of UCG at 975 nm in the presence of fluorescein (FL) and pentamethyldiethylene triamine (PMDETA). FL excited by light emitted from the UCG undergoes electron‐transfer reactions with PMDETA to form free radicals capable of initiating polymerization of methyl methacrylate. To execute the corresponding free‐radical‐promoted cationic polymerization of cyclohexene oxide, isobutyl vinyl ether, and N ‐vinyl carbazole, it was necessary to use FL, dimethyl aniline (DMA), and diphenyliodonium hexafluorophosphate as sensitizer, coinitiator, and oxidant, respectively. Iodonium ions promptly oxidize DMA radicals formed to the corresponding cations. Thus, cationic polymerization with efficiency comparable to the conventional irradiation source was achieved.     

Enantiospecific Trifluoromethyl‐Radical‐Induced Three‐Component Coupling of Boronic Esters with Furans

In the presence of trifluoromethylsulfonium reagents, boronate complexes derived from 2‐lithio furan and non‐racemic secondary and tertiary alkyl or aryl boronic esters undergo deborylative three‐component coupling to give the corresponding 2,5‐disubstituted furans with excellent levels of enantiospecificity. The process proceeds via the reaction of boronate complexes with a trifluoromethyl radical, which triggers 1,2‐metallate rearrangement upon single‐electron oxidation. Alternative electrophiles can also be used in place of trifluoromethylsulfonium reagents to effect similar three‐component coupling reactions.