Water as catalyst and solvent: Tetrahydropyranylation of alcohols in an aqueous medium

Water is found to catalyze the tetrahydropyranylation of alcohols at elevated temperature. Interestingly, tetrahydropyranylation of alcohols works under a wide range of pH, 6.5 to 2 and does not work beyond pH 7.5 in an aqueous medium. Hydrophobic interactions between the substrate alcohol and Dihydropyran ether (DHP) and favorable pKa’s of water, alcohols, and protonated hydroxyl and protonated ethereal functions are the driving forces for the reaction. Thus the reaction, which is carried out in anhydrous aprotic solvents, can be carried out in aqueous medium in an environmentally benign way

Tetrabutylammonium tribromide mediated condensation of carboxylic acids with alcohol

The direct condensation of various carboxylic acids and alcohols was achieved efficiently at reflux temperature under a solvent free condition using a catalytic amount of Tetrabutylammonium Tribromide (TBATB). Chemoselective acylation of primary alcohols in presence of secondary alcohols and phenols has been achieved. Steric factors in carboxylic acids played a crucial role during chemoselective acylation of diols. Reaction under a solvent free condition, absence of any dehydrating agent or use of any special techniques for removal of water and higher yields are the important features of this protocol

Mild and eco-friendly chemoselective acylation of amines in aqueous medium

Amines in the form of amine hydrochlorides are efficiently acylated with anhydrides in an aqueous medium on addition of NaHCO3. Both cyclic and acyclic anhydrides react with equal ease with an amine and amines of various stereo-electronic factors react with the same rates with an anhydride. No chromatographic separation is needed for isolation of the acylated product. Reactions in aqueous medium, innocuous by-products and chemoselective acylation of amines in the presence of phenols and thiols have been achieved with high selectivity

A convenient one-pot synthesis of amines from aldoximes mediated by Koser’s reagent

A simple and convenient procedure has been developed for the synthesis of aromatic amine by a one-pot reaction of aromatic aldoxime with hypervalent iodine(III) reagent [hydroxy(tosyloxy)iodo]benzene (HTIB, Koser’s reagent), in an alkaline medium. The aldoxime reacts with Koser’s reagent to form an intermediate hydroxamic acid, which then undergoes Lossen type rearrangement to produce the desired amine. Several amines have been prepared which otherwise are difficult to prepare, by the reduction of corresponding nitro compounds. The scopes and limitations of this transformation have been discussed

Molecular structures and fluorescence property of Zn(II), Cd(II) complexes of 3-pyridyl-5-aryl-(1 H )-1,2,4-triazoles

The reaction of two 3-pyridyl-5-aryl substituted 1,2,4-triazole ligands (trz-1 and trz-2) with M(NO₃)₂ and MCl₂ (M = Zn^II/Cd^II) afforded the metal complexes [Zn(trz-1)Cl₂], [Cd(trz-1)₂(NO₃)₂] and [M^II(trz-2) ₂](NO₃)₂•H₂O (M = Zn, Cd). The reaction of Cd(NO₃)₂, trz-2 and NaNCS in a 1:1:1 M ratio resulted in the formation of the complex [Cd(trz-2) ₂(NCS)₂]. These complexes have been characterized by spectroscopic analyses and X-ray crystallography. The crystal structures of the complexes show the presence of classical as well as non-classical C–H⋯O, C–H⋯F and C–H⋯S hydrogen bonds, along with a strong π⋯π interaction between the triazole moieties. The complexes exhibit strong fluorescence emissions both in the solid state and in DMSO solution. Further, the intraligand charge transfer origin of the emission in these complexes has been confirmed by DFT and TD-DFT studies

Access to <em>N</em>-Heterocyclic Molecules <em>via</em> Ru(II)-Catalyzed Oxidative Alkyne Annulation Reactions

In last few decades, the transition metal-catalyzed C-H bond activation and alkyne annulation reactions have turned out to be effective methods for the construction of highly important heterocycles. In particular, the Ru(II) catalysts have been used for the oxidative coupling between an internal alkynes and readily available nitrogen directed compounds in a rapid and sustainable manner. The Ru(II) catalysts are very much beneficial due to their stability in both air and water, ease of preparation, inexpensive than those of Rh(III) and designer Co(III) catalysts usually used for alkyne annulation reactions, requirement of mild reaction conditions, and compatible with various oxidants. Owing to these advantages of Ru(II) catalysts herein, we attempt to highlight the recent development in C-H activation and annulation reactions, which lead to the formation of several important N-heterocycles

Thermally Activated Delayed Fluorescence (TADF) Compounds as Photocatalyst in Organic Synthesis: A Metal-Free Greener Approach

Thermally activated delayed fluorescent (TADF) molecules undergo efficient intersystem crossing (ISC) and reverse intersystem crossing (RISC) processes, making them as third-generation emitters in organic light-emitting diodes (OLEDs), photodynamic therapy (PDT) and time-resolved luminescence imaging. Apart from these applications, recently, TADF molecules have been used extensively as photocatalysts in light-mediated synthesis. In general, highly expensive complexes of Rh, Ir, Ru and organic dyes (Eosin Y, Rose Bengal, 9-mesityl-10-methylacridinium perchlorate [Acr-Mes]+ClO4−) are commonly used in the photocatalysis process. Organic-TADF based molecules help to avoid these costly metal catalysts and frequently used organic dyes, making the reaction economical and greener. This chapter will briefly summarize the photocatalytic properties of organic-TADF compounds in organic synthesis

Supramolecular features of 2-(chlorophenyl)-3-[(chlorobenzylidene)-amino]-2,3-dihydroquinazolin-4(1 H )-ones: A combined experimental and computational study

The molecular structures of two isomeric 2-(chlorophenyl)-3-[(chlorobenzylidene)-amino] substituted 2,3-dihydroquinazolin-4(1H)-ones have been determined via single crystal XRD. Both isomers contain chloro substitutions on each of the phenyl rings and as a result a broad spectrum of halogen mediated weak interactions are viable in their crystal structures. The crystal packing of these compounds is stabilized by strong N−H⋯O hydrogen bond and various weak, non-classical hydrogen bonds acting synergistically. Both the molecules contain a chiral center and the weak interactions observed in them are either chiral self-discriminatory or chiral self-recognizing in nature. The weak interactions and spectral features of the compounds have been studied through experimental as well as computational methods including DFT, MEP, NBO and Hiresfeld surface analyses. In addition, the effect of different weak interactions to dictate either chiral self-recognition or self-discrimination in crystal packing has been elucidated

Hypervalent iodine(III)-mediated oxidation of aldoximes to N-acetoxy or N-hydroxy amides

Treatment of various aliphatic and aromatic aldoximes with the hypervalent iodine(III) reagents (diacetoxyiodo)benzene (DIB) or Koser's reagent [hydroxy(tosyloxy)iodo]benzene (HTIB) gave, respectively, N-acetoxy or N-hydroxy amides in good yields rather than the expected nitrile oxide dimerised product oxadiazole-N-oxides reported to be formed with other oxidising and hypervalent iodine reagents. The acetate or the hydroxyl group of DIB or HTIB attacks on the aryl/alkylnitrile oxides formed in situ, which, upon intramolecular rearrangement, gave the expected N-acetoxy or N-hydroxy amides

Rationalization of weak interactions in two fluorescence active imidazo-[1,5-a]-pyridine derivatives: A combined experimental and computational study

Two bis-bromo substituted imidazo-[1,5-a]-pyridine derivatives IMPY1 and IMPY2were synthesized from a 2:1:2 mixture of ortho/meta-bromobenzaldehyde, 2-cyanopyridine and ammonium acetate. The compounds IMPY1 and IMPY2 exhibit blue fluorescence in both THF and methanol solution and their highly fluorescent nature is revealed by the quantum yields &#934;_F ranging from 9.3 to 10.4%. The crystal structure of the compounds are stabilized by various weak, non-classical hydrogen bonds viz. C−H⋯N, C−H⋯Br and C−H⋯&#960; as well as type II interhalogen and C−Br⋯&#960; halogen bonds. The supramolecular features and electronic property of these compounds have been thoroughly analyzed with the aid of DFT, TD-DFT and Molecular Electrostatic Potential (MEP) analyses