DIBAL-H-mediated N-deacetylation of tertiary amides: synthesis of synthetically valuable secondary amines.

A rapid DIBAL-H-mediated N-deacetylation of tertiary amides is described under mild conditions, affording synthetically valuable secondary amines in good to excellent yields.

Progress on green crosslinking of polysaccharide hydrogels for drug delivery and tissue engineering applications.

Natural polysaccharides are being studied for their biocompatibility, biodegradability, low toxicity, and low cost in the fabrication of various hydrogel devices. However, due to their insufficient physicochemical and mechanical qualities, polysaccharide hydrogels alone are not acceptable for biological applications. Various synthetic crosslinkers have been tested to overcome the drawbacks of standalone polysaccharide hydrogels; however, the presence of toxic residual crosslinkers, the generation of toxic by-products following biodegradation, and the requirement of toxic organic solvents for processing pose challenges in achieving the desired non-toxic biomaterials. Natural crosslinkers such as citric acid, tannic acid, vanillin, gallic acid, ferulic acid, proanthocyanidins, phytic acid, squaric acid, and epigallocatechin have been used to generate polysaccharide-based hydrogels in recent years. Various polysaccharides, including cellulose, alginate, pectin, hyaluronic acid, and chitosan, have been hydrogelized and investigated for their potential in drug delivery and tissue engineering applications using natural crosslinkers. We attempted to provide an overview of the synthesis of polysaccharide-based hydrogel systems (films, complex nanoparticles, microspheres, and porous scaffolds) based on green crosslinkers, as well as a description of the mechanism of crosslinking and properties with a special emphasis on drug delivery, and tissue engineering applications.

N-Heterocyclic carbene-catalysed homoenolate addition reaction to 3-cyano-2-imino-2H-chromenes: synthesis of C4-functionalized 2-amino-3-cyano-4H-chromene.

A diastereoselective N-heterocyclic carbene-catalysed reaction between enal and 3-cyano-2-imino-2H-chromene is described for accessing a new type of C4-functionalized 2-amino-3-cyano-4H-chromene. A wide variety of enals and iminochromenes afforded the desired homoenolate addition product 2-amino-4H-chromenes in good yields and with moderate to good diastereoselectivities.

HFIP-promoted halo-carbocyclizations of N- and O-tethered arene-alkene substrates to access all halo (X = Br, I, Cl)-functionalized tetrahydroquinoline and chroman cores.

A new method for the stereoselective metal-, additive- and oxidant-free Friedel-Crafts-type halo-carbocyclization of N- and O-tethered arene-olefin substrates is reported, involving reaction with a suitable electrophilic halogenating reagent (NXS/DCDMH) in hexafluoroisopropanol. All halo (X = Br, I, Cl)-functionalized tetrahydroquinolines and chromans were obtained in excellent yields and with high levels of diastereocontrol (dr = >99 : 1), and these products were successfully transformed into synthetically useful compounds such as dihydroquinolines and partial or full azahelicene compounds.

Highly Selective and Catalytic C-N Bond Cleavage of Tertiary Sulfonamides: Scope and Mechanistic Insight.

A highly chemoselective C-N bond cleavage reaction of p-methoxybenzyl- (PMB), 3,4-dimethoxybenzyl- (DMB), or cinnamyl-substituted tertiary sulfonamides in the presence of catalytic Bi(OTf)3 is presented. A wide range of sulfonamide substrates smoothly furnished the corresponding C-N bond cleavage products in good to excellent yields. Great efforts have been made to obtain insights into the reaction mechanism based on a series of control experiments and mass spectroscopy.

Chemical modification of xanthan gum through graft copolymerization: Tailored properties and potential applications in drug delivery and wastewater treatment.

Xanthan gum (XG) possesses numerous hydroxyl groups, which are the focal points for graft copolymerization of synthetic monomers. A detailed mechanism of graft copolymerization is of utmost importance in obtaining new materials with desirable attributes. The physicochemical, thermal, and morphological changes gained after graft copolymerization is also described. The graft copolymerization can further improve adsorption efficiency of toxic heavy metals and synthetic dyes from wastewater or industrial effluents. The swelling and pH-sensitivity of graft copolymer are attractive features for the purpose of controlled drug delivery. Despite a plethora of reports, comprehensive reviews on XG-based graft copolymers and their potential applications are scarce. Hence, this review undertakes detailed discussion on the synthesis of XG-based graft copolymer, their properties and potential application in drug delivery and wastewater treatment, which would be interesting for the readers and budding scientists to progress further with polysaccharide research and explore new materials for the intended purposes.

Xanthan gum derivatives: review of synthesis, properties and diverse applications.

Natural polysaccharides are well known for their biocompatibility, non-toxicity and biodegradability. These properties are also inherent to xanthan gum (XG), a microbial polysaccharide. This biomaterial has been extensively investigated as matrices for tablets, nanoparticles, microparticles, hydrogels, buccal/transdermal patches, tissue engineering scaffolds with different degrees of success. However, the native XG has its own limitations with regards to its susceptibility to microbial contamination, unusable viscosity, poor thermal and mechanical stability, and inadequate water solubility. Chemical modification can circumvent these limitations and tailor the properties of virgin XG to fulfill the unmet needs of drug delivery, tissue engineering, oil drilling and other applications. This review illustrates the process of chemical modification and/crosslinking of XG via etherification, esterification, acetalation, amidation, and oxidation. This review further describes the tailor-made properties of novel XG derivatives and their potential application in diverse fields. The physicomechanical modification and its impact on the properties of XG are also discussed. Overall, the recent developments on XG derivatives are very promising to progress further with polysaccharide research.

Fe(OTf)3-catalysed Friedel-Crafts reaction of benzenoid arenes with α,ß-unsaturated carbonyl compounds: easy access to 1,1-diarylalkanes.

A simple and efficient method for the synthesis of 1,1-diarylalkanes via the Friedel-Crafts-type alkylation reaction of electron-rich arenes with cinnamic acid ester derivatives or chalcones is reported. Iron triflate has been found to be the best catalyst for the Friedel-Crafts-type alkylation reaction with α,ß-unsaturated carbonyl compounds. This reaction afforded ß,ß-diaryl carbonyl compounds in good yields (65-93%) and with excellent regioselectivities. Remarkably, this method is also compatible with a variety of indoles to provide 3-indolyl-aryl carbonyl compounds in excellent yields. Great efforts have been made to deduce a plausible reaction mechanism based on isotopic labelling experiments.

N-Heterocyclic carbene-mediated oxidative esterification of aldehydes: ester formation and mechanistic studies.

An unexpected N-heterocyclic carbene-catalyzed esterification of α,ß-unsaturated aldehydes including aromatic aldehydes with reactive cinnamyl bromides in the presence of air oxygen or MnO(2) as an oxidant is described. In the presence of oxygen, halogenated and electron-deficient aldehydes react smoothly to furnish esters in good yields. Great efforts have been made on mechanistic studies to deduce a plausible mechanism, based on the experimental results and isotopic labeling experiment.

Stereoselective one-pot synthesis of oxazolines.

Treatment of alkenes with NBS, a nitrile, NaHCO3 and water in the presence of Cu(OTf)2 or Zn(OTf)2 is reported to furnish oxazolines in one pot and good yields. The reaction is equally applicable to chalcones.

Samarium triflate-catalyzed halogen-promoted Friedel-Crafts alkylation with alkenes.

A versatile and efficient halogen-promoted highly regio- and stereoselective Friedel-Crafts (F-C) alkylation with alkenes has been developed with use of easily available and inexpensive NBS or I2 as the efficient halogen sources. Lewis acids, in particular metal triflates, are found to be effective catalysts for this halogen-promoted F-C alkylation. Among these, Sm(OTf)3 was the best catalyst. Electron-rich arenes smoothly underwent F-C alkylation with a variety of alkenes including alpha,beta-unsaturated carbonyl compounds.

Design and synthesis of chiral N-chloroimidodicarbonates: application to asymmetric chlorination of silyl enol ethers.

New chiral N-chloroimidodicarbonates, which function as efficient chiral chlorinating agents, were designed and synthesized. Among these, C(2)-symmetric (1R,2S,5R)-(-)-menthyl-N-chloroimidodicarbonate 2a provided moderate to good enantioselectivity (up to 40%) for the chlorination of silyl enol ethers to afford alpha-chloroketones only in the presence of a suitable Lewis acid such as Sm(OTf)(3).