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.

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.