Raakhi Gupta

Stereoselective synthesis and antioxidant activity of azabicycloadducts derived from 9,10-phenanthrenequinone

A facile synthesis of sprio{1-aza-bicyclo-[3,3,0]-6-octene-8,1′ -phenanthrene}-2′-ones has been accomplished by [3+2] cycloaddition of azomethine ylide (amy) generated from 9,10-phenanthrenequinone and different secondary cyclic amino acids, namely, thiazolidine-4-carboxylic acid, L-pyrrolidine-2-carboxylic acid (L-proline), and piperidine-2-carboxylic acid (pipecolinic acid) with electron-deficient dipolarophiles in 67%–79% yield. AM1 calculations have been performed to understand the stereochemical course of the cycloaddition. The products have been characterized by elemental analyses and spectroscopic techniques, namely IR, 1H NMR, and 13C NMR spectroscopies as well as mass spectrometry. Some of the synthesized cycloadducts showed moderate antioxidant activity.

Aromaticity of 1,4-dehydrotropylium ion and its mono- and poly-phospha analogues

GRAPHICAL ABSTRACT ABSTRACT The tropylium ion and its mono- and poly-phospha analogues on removal of two hydrogen atoms from 1,4-positions accompanied by the formation of a σ C–C bond afford 1,4-dehydrotropylium ion and its mono- and poly-phospha analogues. Aromaticity of these compounds along with 3-aza-1,4-dehydrotropylium ion, 1,4-dehydrotropilidine and its 3-phospha-analogoue has been investigated at the DFT(B3LYP/6-31+G*) level using geometry, ASE, 1H NMR chemical shifts, NICS and magnetic susceptibility exaltation descriptors. 1,4-Dehydrotropylium ion and its mono- and poly-phospha analogues having up to four P atoms along with 3-aza-1,4-dehydrotropylium ion sustain aromaticity like their parent systems. However, 1,4-dehydrotropilidine and its 3-phospha-analogue are found to be nonaromatic.

Experimental and Theoretical Investigation of the Reaction of Secondary Amines with Maleic Anhydride

The reaction of secondary amines, namely 1-methylpiperazine, pyrrolidine, morpholine, 2-methylpiperidine, and diethylamine, with maleic anhydride has been investigated experimentally and theoretically at the DFT level. Under kinetic control, i.e. at −78°C or −15°C, amines add across the C=O functionality exclusively and the initially formed addition products isomerize to the corresponding N-substituted maleimic acid derivatives. In contrast to the acyclic α,β-unsaturated carbonyl compounds, amine does not add across the C=C functionality in maleic anhydride even under thermodynamic control. This behaviour of maleic anhydride can be rationalized on the basis of the local condensed Fukui functions, which reveal that the carbonyl carbon atoms in maleic anhydride are much harder than in an acyclic α,β-unsaturated carbonyl compound, such as acrolein. This prompts the amines to attack the carbonyl group in maleic anhydride exclusively.

Synergy between Experimental and Theoretical Results of Some Reactions of Annelated 1,3-Azaphospholes

Computational calculations have been used successfully to explain the reactivity of the >C=P- functionality in pyrido-annelated 1,3-azaphospholes. Theoretical investigation at the Density Functional Theory (DFT) level shows that the lone pair of the bridgehead nitrogen atoms is involved in extended conjugation, due to which electron density increases considerably in the five-membered azaphosphole ring. The electron density in the azaphosphole is further enhanced by the presence of an ester group at the 3-position making the >C=P- functionality electron-rich. Thus, 1,3-azaphospholo[5,1-a]pyridine, i.e., 2-phosphaindolizine having ester group at the 3-position only does not undergo Diels-Alder (DA) reaction with an electron rich diene, such as 2,3-dimethyl-1,3-butadiene (DMB). However, an ester group at 1-position acts as electron-sink, due to which transfer of the electron density to the >C=P- moiety is checked and DA reaction occurs across the >C=P- functionality. The coordination of the Lewis acid to the carbonyl group at the 3-position raises the activation barrier, while it is lowered remarkably when it is coordinated to the P atom. Furthermore, the attack of 1,3-butadiene on the Si face of the P-coordinated (o-menthoxy)aluminum dichloride complex is a lower activation energy path. Fukui functions could be used to explain relative reactivities of indolizine and 2-phosphaindolizine towards electrophilic substitution reactions.

Synthesis, characterization, and insecticidal activity of new tin (IV) complexes

GRAPHICAL ABSTRACT ABSTRACT A three-component reaction of dimethyltin dibromide with imidazo[1,2-a]pyridine, pyridine derivatives, or isoquinoline and allyl bromide in refluxing ethanol affords the ionic complex, bis(1-allylcycloiminium) dimethyltetrabromostannate (II). The reaction involves N-allylation of cycloimine accompanied by the coordination of two bromide ions with the tin atom of dimethyltin dibromide. The complexes have been characterized by infrared and 1H NMR, 13C NMR, and 119Sn NMR studies. The X-ray crystal structure analysis of a complex reveals the tin atom to be hexacoordinated and the dimethyltetrabromostannate (II) anion having octahedral geometry. Some of the complexes tested for their insecticidal activity are found to exhibit strong activity against Tribolium castaneum insect with LC50 ranging from 0.4 to 0.8 ppm.