Photochemical Synthesis of 7,12-Dioxa[8]helicene and Density Functional Theory Studies: Unravelling the One-Way Valve System Involving Steric Crowding and Aromatic Stability.

symmetric chiral 7,12-dioxa[8]helicenes were synthesized through a series of photochemical - isomerization, electrocyclic reaction, and oxidation steps in a stepwise sequential manner at both the ends of 2,9-di(()-styryl)naphtho[2,1-b:7,8-b']difuran. The chemical transformations complemented with density functional theory (DFT) studies delineate some fundamental concepts, exhibiting counter current effects, namely, destabilization caused by increasing steric crowding and stabilization caused by aromatic units on the overall transformation. The calculated energy profile diagram unravels the formation of photoinduced intermediate species with increasing free energies for the - isomerization and the electrocyclic reactions; the reverse processes for the said steps are prevented by a specific barrier-less oxidation step forming aromatic rings, presenting a one-way valve situation.

Switching the on-surface orientation of oxygen-functionalized helicene.

Helicenes represent an important class of chiral organic material with promising optoelectronic properties. Hence, functionalization of surfaces with helicenes is a key step toward new organic materials devices. The deposition of a heterohelicene containing two furano groups and two hydroxyl groups onto copper(111) surface in ultrahigh vacuum leads to different adsorbate modifications.

Synthesis of Concave and Vaulted 2-Pyran-Fused BINOLs and Corresponding [5] and [7]-Oxa-helicenoids: Regioselective Cascade-Concerted Route and DFT Studies.

Synthesis of concave and vaulted 2-pyran-fused BINOLs has been achieved. A regioselective, path-breaking concerted cascade route allows the placement of six-membered heteroaromatic rings at the sterically crowded 7,8 and 7',8' positions of BINOL. DFT studies with relative energetics that support the kinetically controlled reaction pathway are preferred, matching the experimental results.

Directional Approach to Enantiomerically Enriched Functionalized [7]Oxa-helicenoids and Groove-Based Selective Cyanide Sensing.

Several regioselective functionalized mono- and disubstituted [7]oxa-helicenoids have been synthesized in the enantiomerically enriched (90-99% ee) form. These functionalized helicenoids exhibited pronounced spectral and chiroptical properties suitable for sensing applications. In particular, corresponding helicenoid's mono and dialdehydes have been effectively used as chemodosimeters for selective detection of cyanide anions over other anions, while simple aromatic aldehydes do not function as cyanide sensors.

Benzyne-Mediated Nonconcerted Pathway toward Synthesis of Sterically Crowded [5]- and [7]Oxahelicenoids, Stereochemical and Theoretical Studies, and Optical Resolution of Helicenoids.

Synthesis of [5]- and [7]oxahelicenoids via Diels-Alder reaction of sterically crowded bichromenes with benzyne is presented. Studies carried out on Diels-Alder addition product establish the unusual preference for a stepwise mechanism over the concerted reaction pathway. This high yielding general synthetic protocol affords unexpected anti cycloadducts [5]- and [7]oxahelicenoids, as confirmed by crystallographic analysis.

Sui Generis Helicene-Based Supramolecular Chirogenic System: Enantioselective Sensing, Solvent Control, and Application in Chiral Group Transfer Reaction.

A novel dioxa[6]helicene-based supramolecular chirogenic system () as a specific chiral recognition host for enantiopure -1,2-cyclohexanediamine () is reported. Host with an inherent free phenolic group and a (1)-camphanate chiral handle on the opposite terminal rings of the helicene chromophore acted as an efficient turn on fluorescent sensor for ,- with an excellent enantioselective factor, α = / = 6.3 in benzene.

Tailor-Made Supramolecular Chirogenic System Based on Cs-Symmetric Rigid Organophosphoric Acid Host and Amino Alcohols: Mechanistic Studies, Bulkiness Effect, and Chirality Sensing.

A Cs-symmetric, rigid, achiral organophosphoric acid host with differentiable tautomeric structures has been developed for induced circular dichroism (ICD) studies of vicinal amino alcohols. The structural features of the host and the substituent bulkiness of the guest, together, decide the preferred mode of hydrogen binding on equilibration with a resultant ICD signal. An unequivocal rule correlating the absolute configuration of the guest amino alcohol with the ICD outcome is proposed.

Size-Induced Chiral Discrimination Switching by (S)-(-)-2(α-Hydroxyethyl)Benzimidazole-Derived Azacrowns.

(S)-(-)-2-(α-Hydroxyethyl)benzimidazole (1)-derived diastereomeric monoaza-[18]crown-6 compounds 5 and 6 were synthesised with an additional chiral centre bearing a phenyl ring. The aim was to achieve enhanced enantioselective discrimination, compared with monoaza-[15]crown-5 (7). Surprisingly, reversal of enantioselective binding for chiral guest enantiomers between the two differently sized [15]crown-5 and [18]crown-6 azacrowns were discovered; all three were prepared from the same parent compound, 1.

Asymmetric Diels-Alder reaction involving chiral benzimidazoles as organocatalysts.

(S)-(-)-2-(α-hydroxyethyl)-benzimidazole and (S)-(+)-2-(α-hydroxybenzyl)-benzimidazole work as chiral Brønsted bases (BBs) in Diels-Alder reaction between anthrone and maleimides under mild reaction condition. These chiral BBs cause asymmetric induction.

Ceruloplasmin as a marker of occupational copper exposure.

Estimation of serum copper to indicate copper status in the human system in the context of moderate chronic occupational copper exposure requires a sophisticated and expensive method. Hence, a search for a suitable marker has been made and few studies have found potential in serum ceruloplasmin. In this context, the present study was initiated to explore whether ceruloplasmin could serve as a predictor of occupational copper exposure.

Enantioselective benzoylation of alpha-amino esters using (S)-1-benzoyl-2- (alpha-acetoxyethyl)benzimidazole, a chiral benzimidazolide.

A new chiral benzimidazolide is developed as a nonenzymatic acylating agent for enantioselective benzoylation of racemic alpha-amino esters. The process is highly efficient, which exhibits uniformly high enantioselectivity for alpha-amino esters with or without aryl substituents under mild reaction conditions. The chiral benzimidazolide is inexpensive and is easily accessible.

Furo-fused BINOL based crown as a fluorescent chiral sensor for enantioselective recognition of phenylethylamine and ethyl ester of valine.

A furo-fused BINOL based chiral crown was developed as an enantioselective chiral sensor for phenylethylamine and ethyl ester of valine. Fusion of furan to BINOL has resulted in a highly stereo-discriminating backbone for the chiral crown developed. This chiral crown exhibited a fluorescence enhancement difference of 2.

Aluminum chloride-mediated kinetic resolution of racemic gamma-substituted-gamma-lactones.

Preparation of chiral gamma-substituted-gamma-lactones (1) through kinetic resolution is described. (S)-(-)-1-Phenylethylamine (2) in the presence of anhydrous AlCl(3) shows satisfactory levels of enantioselection in reaction with racemic gamma-substituted-gamma-lactones 1, where (R)-1 remains unreacted, while (S)-1 is enantioselectively converted to the ring-opened amide (S,S)-4. The enantiopurity of (R)-(+)- gamma-substituted gamma-lactones recovered ranges from 62-98% ee.