Microwave-Mediated Modification of Selected Limonoids with DMAB Reagent and Antibacterial Studies

N,N-Dimethylaniline.borane (DMAB) is a stable, multifaceted electrophilic boron agent that displays hydroboration of C = C as well as selective reduction of functional groups under reflux, microwave, and ultrasound conditions. Natural products contain a plethora of functional groups that govern the specific bioactivity. It will be interesting to correlate the change in a functional group with the concern for change in bioactivity. Current research emphasizes the influence of microwave irradiation on moderately reactive DMAB reagent towards the functional group modification of selected limonoid-phytochemicals of Meliaceae family viz. cedrelone, azadirone, nimbin, and azadiradione. DMAB conveniently reduces the ketone, epoxide group into alcohol, and does a hydroboration reaction on the C = C bond. It does not show interest to reduce the ester group irrespective of 30 min of MW irradiation. Except for these reducing properties, the reagent DMAB unveils chemo-selective nature in respect of different functional groups and utilizes in an asymmetric synthesis. The coalescence of amine.borane with microwave irradiation brings forth a commodious and prompt method for the selective reduction of functional groups. The bioactive efficacy of modified phytochemicals is further taken for the antimicrobial studies.     

Additive‐Free Gold(III)‐Catalyzed Stereoselective Synthesis of 2‐Deoxyglycosides Using Phenylpropiolate Glycosides as Donors

Stereoselective synthesis of deoxyglycosides has been achieved from benchtop stable and easily synthesizable deoxy‐phenylpropiolate glycosides (D‐PPGs) using gold(III) salt as catalyst under external additive‐free conditions. Under a simple catalytic system, D‐PPGs reacted with a variety of sugar and non‐sugar acceptors to produce majorly α‐stereoselective O/N‐deoxyglycosides in good to excellent yields and regenerate easily separable and reusable phenylpropiolic acid. Deoxy‐PPGs containing armed and disarmed groups survived well under the optimized reaction conditions. In addition, the orthogonal nature of D‐PPGs was showcased, and 1,1′‐linked trehalose‐type sugar was also synthesized.     

Visible-light mediated regioselective approach towards synthesis of 7-aroyl-6-methyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines

The first visible-light mediated, simple, efficient and ecofriendly protocol for the regioselective synthesis of novel [1,2,4]triazolo[3,4-b][1,3,4]thiadiazines has been developed by the reaction of α-bromodiketones, generated in situ by the bromination of a diverse array of β-diketones with N-bromosuccinimide, with 4-amino-[1,2,4]triazole-3-thiols. The methodology does not require the presence of any additives and this reaction proceeded in the presence of EDG (OMe), EWG (Cl) and heteroarenes (thiophenyl) giving the expected products in good to excellent yields. A solvent free protocol was also established to accomplish the synthesis of target compounds but it required PTSA as a catalyst and yields are comparatively poor. The structure of the regioisomer has been confirmed unambiguously by heteronuclear 2D-NMR [(¹H-¹³C) HMBC, (¹H-¹⁵N) HMBC, (¹H-¹³C) HMQC] spectroscopic and X-ray crystallographic studies.     

Visible-Light-Driven Strain-Increase Ring Contraction Allows the Synthesis of Cyclobutyl Boronic Esters

There are a limited number of ring-contraction methodologies which convert readily available five-membered rings into strained four-membered rings. Here we report a photo-induced radical-mediated ring contraction of five-membered-ring alkenyl boronate complexes into cyclobutanes. The process involves the addition of an electrophilic radical to the electron-rich alkenyl boronate complex, leading to an α-boryl radical. Upon one-electron oxidation, ring-contractive 1,2-metalate rearrangement occurs to give a cyclobutyl boronic ester. A range of radical precursors and vinyl boronates can be employed, and chiral cyclobutanes can be accessed with high levels of stereocontrol. The process was extended to the preparation of benzofused cyclobutenes and the versatility of the boronic ester was demonstrated by conversion to other functional groups.     

Alkaline Stability of Low Oxophilicity Metallopolymer Anion-Exchange Membranes

Anion-exchange membrane fuel cells (AEMFCs) are promising energy conversion devices due to their high efficiency. Nonetheless, AEMFC operation time is currently limited by the low chemical stability of their polymeric anion-exchange membranes. In recent years, metallopolymers, where the metal centers assume the ion transport function, have been proposed as a chemically stable alternative. Here we present a systematic study using a polymer backbone with side-chain N-heterocyclic carbene (NHC) ligands complexed to various metals with low oxophilicity, such as copper, zinc, nickel, and gold. The golden metallopolymer, using the metal with the lowest oxophilicity, demonstrates exceptional alkaline stability, far superior to state-of-the-art quaternary ammonium cations, as well as good in situ AEMFC results. These results demonstrate that judiciously designed metallopolymers may be superior to purely organic membranes and provides a scientific base for further developments in the field.     

Butylated hydroxy benzylidene ring: an important moiety for antioxidant synergism of semicarbazones

Journal of Thermal Analysis and Calorimetry - The compounds having two or more antioxidant functions in their structure exhibit antioxidant synergism that generally increase the antioxidant...     

Triple-Bond Directed Csp2−N Bond Formation with N-Fluorobenzenesulfonimide as Aminating Source: One-Step Transformation of Aldehydes into Amines

A metal-free, versatile triple-bond directed approach for the decarbonylative C−H amination of ortho-alkynyl quinoline/pyridine aldehydes using N-fluorobenzenesulfonimide as nitrogen source under mild reaction conditions has been described. The designed reaction strategy was triggered by trapping of fluorine by base with subsequent attack of bis(phenylsulfonyl)-λ²-azane on the carbonyl carbon of a heterocycle, which was gradually converted into the corresponding amine through a Curtius type rearrangement. This protocol provides a one-step approach for the conversion of aldehydes into amines in good yields. The synthesized amines were successfully transformed into biologically important pyrroloquinolines/pyridines.     

Differential Graded Contact Geometry and Jacobi Structures

We study contact structures on nonnegatively graded manifolds equipped with homological contact vector fields. In the degree 1 case, we show that there is a one-to-one correspondence between such structures (with fixed contact form) and Jacobi manifolds. This correspondence allows us to reinterpret the Poissonization procedure, taking Jacobi manifolds to Poisson manifolds, as a supergeometric version of symplectization.