Mohammed I.M. Wazeer

The regiochemistry and stereochemistry of 1,3-dipolar cycloaddition of cyclic nitrones

Abstract A comparative study of the regio- and stereo-chemical behaviour of the 1,3-dipolar cycloaddition of a series of alkenes with 1-pyrroline 1-oxide and 2,3,4,5-tetrahydropyridine 1-oxide has been carried out. The high degree of both regio- and stereochemical control observed in these reactions has been explained in terms of frontier orbital interaction, steric factors, and secondary orbital interaction in the transition state. While most common alkenes (both mono- and 1,1-di-substituted) gave 2-substituted cycloadducts, highly polarized alkene dimethyl methylenemalonate afforded mainly regioisomeric 3-substituted cycloadduct. Significant secondary orbital interaction is observed with the non-conjugated substituents, hydroxymethyl and its derivatives.

Reactivity, regiochemistry, and stereochemistry of a cyclic nitrone and its α-keto derivative in 1, 3-dipolar cycloaddition reactions

Abstract Rate constants for the cycloadditions of 3,4,5,6-tetrahydropyridine 1-oxide ( 1 ) , and 3-oxo-3,4,5,6-tetrahydropyridine 1-oxide ( 2 ) to several mono- and disubstituted alkenes have been determined at 36°C by 1H NMR Spectroscopy. Small solvent effect on the rate constant indicate the concerted nature of the reaction. It is found that nitrone 2 reacts slower than 1 because of the presence of bond opposition strain in the transition state for the former nitrone. Addition rates are influenced by the dipole moments of the nitrones. Reactivity of these addition reactions usually follows the prediction of frontier orbital approximation. Both the nitrones exhibit very similar regiochemical and stereochemical properties. Significant secondary orbital interaction is observed with several electron deficient alkenes. However, maleic anhydride is found to undergo addition predominantly via exo mode of attack.

Synthesis and aqueous phase behaviour of homo- and copolymers of 1,1-diallyl-4-formylpiperazinium chloride

The quaternary ammonium salt, 1,1-diallyl-4-formylpiperazinium chloride (3) on cyclopolymerization in water solution in the presence of t-butylhydroperoxide gave water soluble polymer (5). The copolymers of (3) with sulfur dioxide have been prepared in DMSO solvent using ammonium persulfate as the initiator. The composition and phase diagram of the aqueous two-phase systems of the homopolymer (5) and copolymer (8) has been studied for the first time for this class of polymers. Synthesis of the polymer (8) paves the way for the preparation of a new class of polymers with a basic trivalent nitrogen as well as a quaternary nitrogen.

Complexation of Zn(II), Cd(II) and Hg(II) with thiourea and selenourea: A 1H, 13C, 15N, 77Se and 113Cd solution and solid-state NMR study

Zinc(II), cadmium(II) and mercury(II) complexes of thiourea (TU) and selenourea (SeU) of general formula M(TU)2Cl2 or M(SeU)2Cl2 have been prepared. The complexes were characterized by elemental analysis and NMR (1H, 13C, 15N, 77Se and 113Cd) spectroscopy. A low-frequency shift of the C=S resonance of thiones in 13C NMR and high-frequency shifts of N–H resonances in 1H and 15N NMR are consistent with sulfur or selenium coordination to the metal ions. The Se nucleus in Cd(SeU)2Cl2 in 77Se NMR is deshielded by 87 ppm on coordination, relative to the free ligand. In comparison, the analogous Zn(II) and Hg(II) complexes show deshielding by 33 and 50 ppm, respectively, indicating that the orbital overlap of Se with Cd is better. Principal components of 77Se and 113Cd shielding tensors were determined from solid-state NMR data.

Peracid oxidation of 1-oxa-8-azabicyclo [3,3,0] octanes: An entry to the cis-2,5-disubstituted pyrrolidines.

Abstract Aldonitrones ( 3 ), generated by peracid induced ring opening of substituted 1-oxa-8-azabicyclo [3.3.0] octane ( 2 ), upon undergoing second cycloa

Cycloaddition of 5-substituted 1- pyrroline 1-oxide and conversion of the nitrone cycloadducts into cis-and trans- 2,5-disubstituted pyrrolidines

Abstract A study of the regiochemical behaviour of the oxidation of 2-substituted-1-hydroxypyrrolidines (2) being to aldo- and kito-nitrones has been carried out. The mechanism of the peracid induced ring opening reaction of isoxazolidines (5) is now firmly established. Second cycloaddition reaction of 5-substituted 1- pyrroline 1-oxide (6) provides an efficient and stereoselective entry into the trans- (24) as well as cis-2,5- disubstituted pyrrolidines (28).

13C, 15N AND 31P NMR STUDY OF THE DISPROPORTIONATION OF CYANOGOLD(I) COMPLEXES : R3PAU13C15N

Abstract The disproportionation of cyanogold(I) complexes of general formula [R 3 PAu 13 C 15 N] forming [(R 3 P) 2 Au] + and [Au( 13 C 15 N) 2 ] − ions has been investigated using 13 C, 15 N and 31 P NMR spectroscopy for a series of phosphines with R=cyclohexyl, i -propyl, Et, Me, cyclohexyl/diphenyl, o -tolyl, p -tolyl, m -tolyl, p -tolyl/diphenyl, allyl/diphenyl, phenyl, tri(cyanoethyl) CEP, and 1-naphthyl. The 13 C NMR of the 13 C 15 N group in these complexes exhibited two distinct resonances, one due 13 C in the starting [R 3 PAu 13 C 15 N] complex and the second in the [Au( 13 C 15 N) 2 ] − anion. The 31 P NMR spectra revealed two 31 P resonances due to [R 3 PAu 13 C 15 N] complex, and the [(R 3 P) 2 Au] + cation. The 15 N NMR revealed only an averaged resonance due to [R 3 PAu 13 C 15 N] and [Au( 13 C 15 N) 2 ] − anion, except in the cases of [Me 3 PAu 13 C 15 N] and [Et 3 PAu 13 C 15 N] where two resonances were observed. The coupling constants, 1 J( 13 C– 15 N), 2 J( 31 P– 13 C) and 3 J( 31 P– 15 N) were obtained for all complexes and the free energies of activation for ligand disproportionation were determined using 31 P–{ 1 H} NMR band shape analysis.

The 13-dipolar cycloaddition reactions of 3456-tetrahydro-2h-azepine 1-oxide.

Abstract A study of the regio- and stereo-chemical behaviour of the 13-dipolar cycloaddition of 3456-tetrahydro-2H-azepine 1-oxide with a series of di- and tri-substituted alkenes has been carried out. Significant secondary orbital interactions are observed in the addition reaction of alkenes having conjugated methoxycarbonyl substituents or having oxygen at allylic or homoallylic position. Quite unexpectedly the addition of crotonate and cinnamate esters are found to be non-unidirectional.

The 1,3-dipolar cycloaddition of cyclic nitrones with 1,2-disubstituted alkenes

Abstract A comparative study of the stereochemical behaviour of the 1,3-dipolar cycloaddition of a series of 1,2-disubstituted alkenes with 1-pyrroline 1-oxide ( 1 ) and 2,3,4,5-tetrahydropyridine 1-oxide ( 2 ) has been carried out. Both the nitrones exhibit very similar stereochemical properties. Rate constants for the cycloaddition of these nitrones to several disubstituted alkenes have been determinded at 36°C by 1 H n.m.r. spectroscopy. It is found that the nitrone 1 reacts slower than 2 due to the presence of bond eclipsing strain in the transition state involving 1 .

Regiochemistry of mercury(II) oxide oxidation of unsymmetrical N,N-disubstituted hydroxylamines

Abstract Mercury(II) oxide oxidation of N,N-disubstituted hydroxylamines with the α and α′ carbon atoms containing one and two hydrogen atoms, respectively, gave aldonitrones in a highly regioselective manner. Removal of the α proton is involved in the rate determining step as shown by primary kinetic isotope effect.