Isolation and characterization of some flavonoids from the leaf of Tapinanthus globiferus growing on Acacia nilotica

Tapinanthus globiferus is used ethnomedicinally for the treatment of bacterial infections, inflammation, stomach pain, ulcers among others. The aim of the study was to isolate bioactive compounds from the leaf of T. globiferus growing on Acacia nilotica. The powdered plant material was extracted with 90 % methanol using cold maceration and the resulting crude methanol leaf extract was partitioned into n-hexane, chloroform, ethylacetate and n-butanol fractions. The ethylacetate fraction was chromatographed on a silica gel, sephadex LH-20 column and preparative thin-layer chromatography. (-)-Epicatechin and Quercetin 3-O-β-D-glucopyranoside were isolated and characterized by means of physiochemical and spectroscopic (1D and 2D-NMR) analyses for the first time from T. globiferus growing on A. nilotica. Keywords:  Tapinanthus globiferus; Flavonoids; Isolation; NM

Borrowing hydrogen for organic synthesis

Borrowing hydrogen is a process that is used to diversify the synthetic utility of commodity alcohols. A catalyst first oxidizes an alcohol by removing hydrogen to form a reactive carbonyl compound. This intermediate can undergo a diverse range of subsequent transformations before the catalyst returns the “borrowed” hydrogen to liberate the product and regenerate the catalyst. In this way, alcohols may be used as alkylating agents whereby the sole byproduct of this one-pot reaction is water. In recent decades, significant advances have been made in this area, demonstrating many effective methods to access valuable products. This outlook highlights the diversity of metal and biocatalysts that are available for this approach, as well as the various transformations that can be performed, focusing on a selection of the most significant and recent advances. By succinctly describing and conveying the versatility of borrowing hydrogen chemistry, we anticipate its uptake will increase across a wider scientific audience, expanding opportunities for further development

Iron‐catalyzed borrowing hydrogen C‐Alkylation of oxindoles with alcohols

A general and efficient iron-catalyzed C-alkylation of oxindoles has been developed. This borrowing hydrogen approach employs a (cyclopentadienone)iron carbonyl complex (2 mol %) and exhibits a broad reaction scope, allowing benzylic and simple primary and secondary aliphatic alcohols to be employed as alkylating agents. A variety of oxindoles undergo selective monoC(3)-alkylation in good to excellent isolated yields (28 examples, 50- 92% yield, 79% average yield)

Exploring the borrowing hydrogen methodology using earth abundant metals

This thesis describes the development of new catalytic methodologies in borrowing hydrogen chemistry also known as hydrogen auto transfer, which is a sub-class of transfer hydrogenation chemistry. The main aim was to develop new catalytic methods via the borrowing hydrogen process using earth abundant metals like iron, mangane or cobalt. The second chapter of this thesis discusses the iron catalysed C(3)-alkylation of oxindole with alcohols via the borrowing hydrogen process using iron complex as the catalysts. Oxindole framework is found in many pharmacologically active compounds. It underwent selective C(3)- mono-alkylation with a wide range of simple aliphatic, benzylic and heteroaryl alcohols in good to excellent yield (28 examples, 79% average yield). The mechanistic study revealed the presence of reactive carbonyl intermediate and a metal hydride probing the borrowing catalytic process. In chapter three, the first transition metal C-alkylation of aryl ketones with secondary alcohols using only base was discussed. The method employed a bulky and sterically hindered substrate as the ketone, establishing a route for the synthesis of β-substituted carbonyl compounds with different secondary alcohols, giving a wide range of products with good yield (23 examples, 65% average yield). From the mechanistic study it was proposed that the reaction proceeds via an oppenauer-type oxidation of secondary alcohol followed by selective cross aldol�condensation and then the subsequent Meerwein-ponndorf-Verley (MPV)-type reduction of the enone. In the final research chapter, chapter four, the enantioselective N-alkylation of amines with secondary alcohols was investigated and the desired products was obtained in an excellent yield albeit with no any e.e vi and the isomerization/alkylation reaction of epoxy styrene with primary alcohols was also investigated but no any meaningful results was obtained from the pilot study

Transition metal free α-C-alkylation of ketones using secondary alcohols

A base-mediated α-C-alkylation of ketones with secondary alcohols has been developed. This transition metal free approach employs KOt-Bu as the base and exhibits a broad scope, allowing a range of commodity aliphatic secondary alcohols and 1-arylethanols to be employed as alkylating agents. Aryl methyl ketones undergo selective mono-α-C-alkylation in high isolated yields (23 examples, 65% average yield)