Santosh G. Tilve

Recent developments in the synthesis of five- and six-membered heterocycles using molecular iodine

Heterocyclic scaffolds represent the key structural subunits of many biologically active compounds. Over the last few years iodine-mediated reactions have been extensively studied due to their low cost and eco-friendliness. This Review covers advances in the field of iodine-mediated synthesis of heterocyclic compounds since 2006, especially with an emphasis on mechanisms of ring formation. In this article, syntheses of different heterocycles are classified based on the manipulation of functional groups.

Advancement in methodologies for reduction of nitroarenes

The importance of aryl amines as raw materials for various applications has spurred extensive research in developing economic processes for the reduction of nitroarenes. Developing green methodologies is now a compelling discipline for synthetic organic chemists. The recent surge in nanochemistry has led to the development of some interesting applications in nitro reduction processes. This review discusses some recent examples of reports in this field. The different methods are classified based on the source of hydrogen utilized during reduction and the mechanism involved in the reduction process.

Recent advances in the synthesis of naturally occurring pyrrolidines, pyrrolizidines and indolizidine alkaloids using proline as a unique chiral synthon

The present article describes the synthesis of a wide spectrum of natural products of the class pyrrolidines, pyrrolizidines and indolizidines using proline as a viable synthetic precursor. The review emphasizes the versatility of the basic unit of proline as a useful chiral synthon confined for the synthesis of only natural products of the above mentioned families. The vast coverage of the synthesis of these natural products is presented for a period from 1990 onwards. The synthesis of all ranges of alkaloids from simple to complex molecules is presented under the groups of alkaloids.

An expeditious I2-catalyzed entry into 6H-indolo[2,3-b]quinoline system of cryptotackieine.

A synthesis of a series of novel 6H-indolo[2,3-b]quinolines with different substituents on the quinoline ring is described. The method involves reaction of indole-3-carboxyaldehyde with aryl amines in the presence of a catalytic amount of iodine in refluxing diphenyl ether to yield indolo[2,3-b]quinolines in one-pot. The present approach provides a new route for the synthesis of polycyclic structures related to an alkaloid cryptotackieine (neocryptolepine).

Isolation, Biological Activities and Synthesis of Indoloquinoline Alkaloids: Cryptolepine, Isocryptolepine and Neocryptolepine

The tetracyclic heteroaromatic compounds cryptolepine, isocryptolepine and neocryptolepine are all naturally occurring indoloquinoline alkaloids isolated from the shrub Cryptolepis sanguinolenta and are important due to their wide spectrum of biological properties. This review describes the isolation, brief biological activities and various synthetic methodologies developed during recent years for the preparation of this important class of alkaloids, with special emphasis on preparation and properties of cryptolepine 1, isocryptolepine 2 and neocryptolepine 3.

Tandem Wittig−Ene Reaction Approach to Kainic Acid

The first example of a tandem Wittig-intramolecular ene reaction approach and its application toward the synthesis of kainic acid is reported. The synthetic pathway involves conversion of prenyl bromide into phosphorane 3, followed by one-pot Wittig olefination and an ene reaction with glyoxalic acid to give the cis fused pyrrolidine skeleton of kainic acid.

Graphite catalyzed solvent free synthesis of dihydropyrimidin-2(1H)-ones/thiones and their antidiabetic activity.

A solvent free three component condensation reaction between an aldehyde, ethyl acetoacetate and urea catalyzed by graphite, a green catalyst is described for the synthesis of dihydropyrimidin-2(1H)-ones. This protocol is scalable and the catalyst is reusable. This method is also applied for the synthesis of dihydropyrimidin-2(1H)-thiones. α-Amylase, a key enzyme in carbohydrate metabolism is generally targeted for management of type 2 diabetes. The therapeutic potential of the dihydropyrimidinones and dihydropyrimidinthiones to inhibit α-amylase activity was evaluated by in vitro assay. Of the synthesized compounds 3,4-dihydropyrimidin-2(1H)-thione (1k) demonstrated highest inhibition of α-amylase activity.

Total synthesis of (-)- and (+)-tedanalactam

The first stereoselective route providing access to both enantiomers of tedanalactam, a naturally occurring piperidone, has been developed. The stereogenic centers were generated by the use of Sharpless asymmetric dihydroxylation. Tandem oxidation-Wittig reaction and one-pot deprotection, lactamization, and oxirane ring formation are the other key elements.

Iodine-Mediated Intramolecular Dehydrogenative Coupling: Synthesis of N-Alkylindolo[3,2-c]- and -[2,3-c]quinoline Iodides

An I2/TBHP-mediated intramolecular dehydrogenative coupling reaction is developed for the synthesis of a library of medicinally important 5,11-dialkylindolo[3,2-c]quinoline salts and 5,7-dimethylindolo[2,3-c]quinoline salts. The annulation reaction is followed by aromatization to yield tetracycles in good yield. This protocol is also demonstrated for the synthesis of the naturally occurring isocryptolepine in salt form.

Magnetically recoverable catalytic Co–Co2B nanocomposites for the chemoselective reduction of aromatic nitro compounds

Magnetically recoverable and recyclable Co–Co2B nanocomposites are described for the catalytic and chemoselective reduction of nitroarenes using two different hydrogen sources, sodium borohydride and hydrazine hydrate. Both the systems display an interesting chemoselective reduction switch. The kinetics of reduction of nitroaromatics were studied for the first time and follow nitroreductase enzyme-like kinetics with exceedingly high Kcat (5.2 × 104 s−1) and Kcat/KM (4.4 × 106 M−1 s−1) values, reaching the state of catalytic perfection. The recyclability of the catalyst system was studied by magnetically recovering the nano composite catalyst.