K. V. Radhakrishnan

Iodine assisted palladium catalyzed ring opening of bicyclic hydrazines with organoboronic acids: stereoselective synthesis of functionalized cyclopentenes and alkylidene cyclopentenes

A novel reactivity of organoboronic acids with bicyclic hydrazines leading to the stereoselective formation of trans-vicinal disubstituted cyclopentenes in good to excellent yield is discussed. The reaction of cyclopentadiene and fulvene derived azabicyclic alkenes with organoboronic acids afforded the trans-3,4-disubstituted cyclopentenes and alkylidene cyclopentenes in good to excellent yields. The products, having a broad range of substituents, are important intermediates in the synthesis of a number of pharmaceutically important molecules.

Palladium/Lewis Acid Mediated Domino Reaction of Pentafulvene Derived Diazabicyclic Olefins: Efficient Access to Spiropentacyclic Motif with an Indoline and Pyrazolidine Fused to Cyclopentene

A palladium/Lewis acid mediated stepwise and one-pot transformation of pentafulvene derived diazabicyclic olefins is described. The reaction offers a facile strategy for the synthesis of novel spiropentacyclic motifs with indoline and pyrazolidine fused to the cyclopentene core.

Titanium‐Catalyzed Hydroalumination of Conjugated Dienes: Access to Fulvene‐Derived Allylaluminium Reagents and Their Diastereoselective Reactions with Carbonyl Compounds

The described titanium-catalyzed hydroalumination of conjugated dienes opens up a new way to allylaluminium reagents. The reaction is carried out by using diisobutylaluminium hydride (DIBAL-H) and a catalytic amount of [Cp2TiCl2] (Cp = cyclopentadienyl). When applied to mono- and disubstitued pentafulvenes, this reaction proceeds in a highly endocyclic manner. The formed allylaluminium compounds react regio- and stereoselectively with both aldehydes and ketones to afford homoallylic alcohols that are suitable synthons for functionalized cyclopentanones. An extension of this methodology to simple dienes was also investigated. In the proposed mechanism, the initially formed bimetallic species (Ti/Al) are involved in the two possible catalytic cycles with a direct hydroalumination or/and a hydrotitanation followed by a titanium to aluminium transmetallation.

Palladium catalyzed reaction of ortho-functionalized aryl iodides with bicyclic hydrazines: facile route toward heteroannulated cyclopentenes and azabicycles

Abstract A palladium catalyzed tandem protocol for the synthesis of cyclopentene fused heterocycles from diazabicyclic alkenes and ortho -functionalized aryl iodides has been elaborated. This tandem protocol was utilized for the synthesis of a number of cyclopentene fused dihydrobenzofurans and indolines. The reaction can be tuned toward the formation of either 3,4-disubstituted cyclopentenes or cyclopentene fused heterocycles by careful manipulation of the reaction parameters. The reaction was also extended to bicyclic alkenes derived from fulvene, which resulted in the heteroannulation of the azabicyclic system.

Mild rhodium(I) catalyzed ring opening of cyclopropane appended spirotricyclic olefins through C–H activation of arylboronic acids

Herein we describe a ligand free rhodium(I) catalyzed stereoselective ring-opening of cyclopropane appended spirotricyclic olefins through C–H bond cleavage of boronic acid. The developed methodology leads to the formation of aromatic molecules functionalized with trans-disubstituted spiro[2.4]hept-4-ene and cyclopropane appended spirotricyclic framework via 1,4-alkyl to aryl rhodium migration.

An exclusive approach to 3,4-disubstituted cyclopentenes and alkylidene cyclopentenes via the palladium catalyzed ring opening of azabicyclic olefins with aryl halides

A simple and efficient method for the stereoselective ring opening of bicyclic hydrazines with various aryl halides under palladium catalysis has been elaborated. The reactions afforded trans-3,4-disubstituted cyclopentenes or alkylidene cyclopentenes in good to excellent yields. By taking advantage of multiple points of functionalization in the synthesized trans-3-phenyl-4-hydrazino-cyclopentene, we have synthesized the antidepressant Cypenamine (trans-2-phenylcyclopentylamine).

Palladium catalyzed 1,8-conjugate addition to heptafulvene via bis-π-allyl palladium complexes.

The palladium catalyzed 1,8-conjugate addition of heptafulvene, an antiaromatic conjugated 8π-electron system, is discussed. The method is utilized for the concise synthesis of bis-functionalized cycloheptatriene (CHT) derivatives. This is the first report on the palladium catalyzed bisfunctionalization of a cyclic cross conjugated system.

OXIDATIVE ADDITION OF 1,3-DICARBONYL COMPOUNDS TO ALKENES MEDIATED BY CERIUM(IV) AMMONIUM NITRATE AND MANGANESE(III) ACETATE : A COMPARATIVE STUDY

The oxidative addition of dimedone, acetylacetone and ethyl acetoacetate to cyclic and acyclic alkenes mediated by CAN gives dihydrofurans in good yields. Similar addition of the radical generated from dimethyl malonate to alkenes provides lactones. A comparative study of these reactions vis-a-vis those mediated by Mn(OAc)3 has shown that the former generally lead to higher yields of products. The milder reaction conditions, experimental simplicity, and the solubility of CAN in common organic solvents like methanol, acetonitrile and THF are other advantages. Thus it appears from this study that CAN is superior to the commonly used Mn(OAc)3.

Comparison of antidiabetic potential of (+) and (−)-hopeaphenol, a pair of enantiomers isolated from Ampelocissus indica (L.) and Vateria indica Linn., with respect to inhibition of digestive enzymes and induction of glucose uptake in L6 myotubes

The remarkable α-glucosidase inhibition exhibited by the acetone extract of the rhizome of Ampelocissus indica (L.) and stem bark of Vateria indica Linn. (IC50 23.2 and 1.47 μg mL−1) encouraged us to isolate the phytochemicals from these plants. (+) and (−)-hopeaphenol (1) and (2) were isolated from A. indica (L.) and V. indica Linn. respectively. Compounds 1 and 2 displayed IC50 values of 21.21 ± 0.987 and 9.47 ± 0.967 μM in an α-glucosidase inhibitory assay. The effect of glucose uptake performed by 2-NBDG in L6 rat skeletal muscle cells using flow cytometry (BD FACS Aria II, USA) showed potent glucose uptake by (+) and (−)-hopeaphenol of 31% and 26.4%, respectively. The data from an MTT cell viability assay revealed that the compounds are not toxic to the cells up to 200 μM. Molecular docking studies show that the compounds bind effectively to the active sites of the proteins 1BVN, 3A4A and 3AJ7, which supported the observed α-glucosidase inhibition. The structures of these compounds were determined by the analysis of various spectroscopic data including HRMS-ESI, 2D NMR, CD spectroscopy, optical activity and were unequivocally established by single crystal X-ray crystallography. Herein we are reporting the phytochemicals from Ampelocissus indica (L.) and their antidiabetic activities for the first time.

Lewis acid catalyzed C-3 alkylidenecyclopentenylation of indoles: an easy access to functionalized indoles and bisindoles

A Lewis acid catalyzed C-3 alkylidenecylopentenylation of indoles through the ring opening of pentafulvene derived diazabicyclic olefins has been developed. The present protocol offers an efficient route toward the synthesis of indole and bisindole derivatives. The role of the hydrazine group, as a reaction carrier in the strategy has also been demonstrated by the stepwise synthesis of functionalized bisindole.