Synthesis of Benzo[1,4]heterocycles using Palladium Catalyzed Heck Reaction to Vinylogous Carbonates/Carbamates: Unexpected Formation of Indoles via Carbopalladation Intercepted by Nucleopalladation

An efficient protocol for the stereoselective synthesis of benzo­[1,4]­heterocycles via palladium catalyzed Heck reaction on <i>o</i>-halo-aryl-o<i>xa</i>/<i>thia</i>/<i>aza</i> tethered vinylogous carbonates/carbamates/esters has been developed. Unexpected formation of indoles is observed when unprotected 2-iodoaniline tethered vinylogous carbonates are subjected to the Heck reaction. Mechanistic studies indicate that formation of these indoles is an outcome of the interception of the carbopalladation step by nucleopalladation. The method can be used to gain rapid access to the core skeleton of abacopterin A–C

Synthesis of Benzo[1,4]heterocycles using Palladium Catalyzed Heck Reaction to Vinylogous Carbonates/Carbamates: Unexpected Formation of Indoles via Carbopalladation Intercepted by Nucleopalladation

An efficient protocol for the stereoselective synthesis of benzo­[1,4]­heterocycles via palladium catalyzed Heck reaction on <i>o</i>-halo-aryl-o<i>xa</i>/<i>thia</i>/<i>aza</i> tethered vinylogous carbonates/carbamates/esters has been developed. Unexpected formation of indoles is observed when unprotected 2-iodoaniline tethered vinylogous carbonates are subjected to the Heck reaction. Mechanistic studies indicate that formation of these indoles is an outcome of the interception of the carbopalladation step by nucleopalladation. The method can be used to gain rapid access to the core skeleton of abacopterin A–C

Lewis Acid Mediated Cascade Friedel–Craft/Alkyne Indol-2-yl Cation Cyclization/Vinyl Cation Trapping for the Synthesis of <i>N</i>‑Fused Indole Derivatives

A Lewis acid promoted cascade Friedel-Craft/alkyne indol-2-yl cation cyclization/vinyl cation trapping for an efficient and divergent synthesis of <i>N</i>-fused indoles is developed. The present study illustrates the first example of an alkyne as a nucleophile on the less explored indol-2-yl cation. The method efficiently affords pharmaceutically important pyrrolizino-quinolines and complex fused indole derivatives in high yields

Cascade Radical Cyclization of <i>N</i>‑Propargylindoles: Substituents Dictate Stereoselective Formation of <i>N</i>‑Fused Indolines versus Indoles

An efficient protocol for the synthesis of pyrrolo­[1,2-<i>a</i>]­indole derivatives having sulfide functionality using cascade radical cyclization on propargylindole is described. The nature of the substituents at the propargylic carbon bearing nitrogen of the indole has a profound effect on the rate, yield, and nature of the product obtained by the cascade radical cyclization. An expeditious one-pot route for cascade radical cyclization–desulfurization is also presented. Products obtained were elaborated to the core of the putative structure of the yuremamine and indoline derivative with five contiguous stereocenters

Lewis Acid Mediated “<i>endo-dig</i>” Hydroalkoxylation–Reduction on Internal Alkynols for the Stereoselective Synthesis of Cyclic Ethers and 1,4-Oxazepanes

Lewis acid mediated 5/6/7-<i>endo-dig</i> hydroalkoxylation–reduction cascade on internal alkynols gave an expedient, stereoselective synthesis of cyclic ethers and 1,4-oxazepanes. The strategy has been extended to the first examples of hydroalkoxylation–alkyne Prins-type cyclization cascade of alkyne-tethered alkynols, giving access to oxa-bicyclic scaffolds. This method was used as the key step in the stereoselective total synthesis of calyxolane A-B, as well as (±)-centrolobine and its homologue

Stereoselective Synthesis of Oxa- and Aza-Angular Triquinanes Using Tandem Radical Cyclization to Vinylogous Carbonates and Carbamates

Tandem radical cyclization to vinylogous carbonates and carbamates is developed for a new, highly stereoselective synthesis of heterocyclic angular triquinanes. The strategy is also useful to gain access to oxa- and azatriquinanes, which incorporate the spiroindoline moiety. The method is further extended to the synthesis of lactone-bearing as well as uracil-fused angular triquinanes

Stereoselective Synthesis of Oxa- and Aza-Angular Triquinanes Using Tandem Radical Cyclization to Vinylogous Carbonates and Carbamates

Tandem radical cyclization to vinylogous carbonates and carbamates is developed for a new, highly stereoselective synthesis of heterocyclic angular triquinanes. The strategy is also useful to gain access to oxa- and azatriquinanes, which incorporate the spiroindoline moiety. The method is further extended to the synthesis of lactone-bearing as well as uracil-fused angular triquinanes

Stereoselective Synthesis of Oxa- and Aza-Angular Triquinanes Using Tandem Radical Cyclization to Vinylogous Carbonates and Carbamates

Tandem radical cyclization to vinylogous carbonates and carbamates is developed for a new, highly stereoselective synthesis of heterocyclic angular triquinanes. The strategy is also useful to gain access to oxa- and azatriquinanes, which incorporate the spiroindoline moiety. The method is further extended to the synthesis of lactone-bearing as well as uracil-fused angular triquinanes

Stereoselective Synthesis of Oxa- and Aza-Angular Triquinanes Using Tandem Radical Cyclization to Vinylogous Carbonates and Carbamates

Tandem radical cyclization to vinylogous carbonates and carbamates is developed for a new, highly stereoselective synthesis of heterocyclic angular triquinanes. The strategy is also useful to gain access to oxa- and azatriquinanes, which incorporate the spiroindoline moiety. The method is further extended to the synthesis of lactone-bearing as well as uracil-fused angular triquinanes

White Light Emission in Butadiyne Bridged Pyrene–Phenyl Hybrid Fluorophore: Understanding the Photophysical Importance of Diyne Spacer and Utilizing the Excited-State Photophysics for Vapor Detection

Generation of white light emission (WLE) from a single organic fluorophore is challenging because of the need to get fluorescence covering the visible region (400–700 nm) upon excitation of the dye at near-ultraviolet wavelength. Herein, we report WLE from a butadiyne bridged pyrene–phenyl hybrid fluorophore in mixed-aqueous solvents as well as in polymer film matrices. The ability of the butadiynyl dye to emit from multiple excited states such as locally excited (LE; 400–500 nm), aggregate (excimer type; 475–600 nm), and charge transfer (CT; 500–750 nm) states spanning the emission almost throughout the visible range has made the generation of the white light to be possible. In highly polar solvent such as acetonitrile, the butadiynyl dye emits from the LE and CT states, and the WLE is achieved through a control of the dye concentration such that intermolecular CT (exciplex type) contributes along with the intramolecular CT and LE emissions. In mixed-aqueous systems such as water–acetonitrile and water–<i>N</i>,<i>N</i>-dimethylformamide, the CT emission is red-shifted (because of the high dielctric constant of water), and the contribution of the aggregate emission (originated because of the poor solvent water) is important in maintaining the relative distribution of the fluorescence intensities (LE, excimer, and CT) in the entire visible region. The significance of the diyne spacer in achieving the WLE is delineated through a control study with a single acetylenic analogue. The LE, aggregate, and CT emissions are involved in generating bluish-white light in a poly­(vinyl alcohol) film matrix of the butadiynyl dye. Blue emission is noted in a poly­(methyl methacrylate) (PMMA) film matrix of the dye with a major contribution from the LE and a minor contribution from the aggregate state. Exposure of the PMMA film of the dye to polar aprotic vapors assists in gaining the CT state emission such that the LE, aggregate, CT emissions cover the entire visible region to produce the WLE. This opens a new strategy for selective vapor sensing