Search results for "regioselectivity."

Reaction of 3-Methylamino-1,2-diols with Dihalomethanes. Synthesis of Chiral 4-Substituted 3-Methyltetrahydro-1,3-oxazin-5-ols

2000

Abstract Enantiomerically pure 4,5-disubstituted 3-methyltetrahydro-1,3-oxazines have been obtained by reaction of 3-methylamino-1,2-diols with dichloromethane by regioselective differentiation of hydroxyl groups.

ChemInform Abstract: Metal-Free Regioselective C-C Bond Cleavage in 1,3,5-Triazine Derivatives of β-Diketones.

2014

The reaction of cyanuric chloride (I) with 3 equivalents of ketones (II) in the presence of 3 equivalents of KOH affords adducts (IV), which are converted into deacylated derivatives (III) by treatment with aqueous HCl solution in MeOH.

Selectively Functionalized Constrained Polyazamacrocycles: Building Blocks for Multifunctional Chelating Agents

2013

A new class of cross-bridged and side-bridged 1,4,7,10-tetraazacyclotridecanes (homocyclens) bearing an aminomethyl pendant arm on the carbon skeleton has been prepared. The regioselectivity of the quaternization of the bis-aminal intermediates is discussed on the basis of X-ray diffraction and NMR experiments. These new polyazamacrocycles are valuable precursors of bifunctional chelating agents for applications in nuclear medicine.

ChemInform Abstract: Palladium-Catalyzed Suzuki Carbonylative Reaction of α-Halomethyl Oxime Ethers: A Regioselective Route to Unsymmetrical 1,3-Oxyi…

2015

Scandium-catalyzed preparation of cytotoxic 3-functionalized quinolin-2-ones: Regioselective ring enlargement of isatins or imino isatins

2012

Trimethylsilyldiazomethane in the presence of catalytic amounts of Sc(OTf) 3 smoothly promotes the ring expansion of isatins or imino isatins to efficiently afford 3-functionalized quinolin-2-ones through controlled ring enlargement. Whereas the ring-expansion reaction of azetidine-2,3-diones led to the adduct resulting from migration of the carbonyl group, the ring-expansion reaction of oxindole derivatives gave the adduct resulting from migration of the aryl group. To rationalize the experimental observations, theoretical studies have been performed. Moreover, the biological activity of some of the synthesized heterocycles has been evaluated in four cancer cell lines. © 2012 Wiley-VCH Ver…

Leaving Group and Regioselectivity Switches in the Aminoalkylation Reaction of Indoles and Related Heterocycles with α-Amido Sulfones

2013

The regioselective aminoalkylation of indoles and related heterocycles with α-amido sulfones under basic conditions has been studied. The reaction that employed the MeMgBr/MgBr2 system provided high yields of 3-(1-carbamoylalkyl)indoles. On the other hand, the reaction that used Cs2CO3 afforded 1-(1-carbamoylalkyl)indoles exclusively in high yields. The first reaction constitutes a switch of the leaving group of the α-amido sulfone in comparison to previously reported reactions between indoles and α-amido sulfones, which provided 3-(1-arylsulfonylalkyl)indoles. The second reaction constitutes a switch in the regioselectivity. The extensions of these C- and N-aminoalkylations starting from p…

A dft study of the regioselectivity in intramolecular diels-alder reactions with formation of a tricyclodecane skeleton

2011

Three different intramolecular Diels-Alder (IMDA) reactions associated with the formation of fused and bridged tricyclodecane skeletons have been studied at the B3LYP/6-31G(d) computational level. While substitution on the diene and dienophile fragments modulates the polar character of the reaction, the strain effect produced by the methylene tether affects the activation energy, and its torsion controls the different regioisomeric channels of the IMDA process. Analysis of the reactivity indices recently proposed (J. Soto-Delgado et al., Org. Biomol. Chem., 2010, 8, 3678) within the conceptual density functional theory allows for the characterization of the mechanism including the charge tr…

Regioselective Glycosylation of Glucosamine and Galactosamine Derivates Using O-Pivaloyl Galactosyl Donors

2003

Penta-O-pivaloyl-galactopyranose and tetra-O-pivaloyl-galactopyranosyl bromide after electrophilic activation reacted with 6-O-protected 2-azido-galactosides to give the precursor structures of the Thomsen-Friedenreich antigen disaccharide with high regioselectivity, but low yield.With 4,6-Obenzylidene protected 2-azidogalactosides and 2-O-pivaloyl phenylthio galactosides, T-antigen disaccharides of this type were obtained in good yields. Glycosylation reactions of 4,6-O-benzylidene protected glucosamine derivatives with O-pivaloyl protected galactosyl bromide efficiently gave lactolactosamine disaccharides. Even a thioglycoside was efficiently galactosylated by this method resulting in the…

Unequivocal determination of isomeric products of reaction between 3-methyl-1-phenyl-2-pyrazoline-4,5-dione and aromatic 1,2-diamines

1999

Abstract Regioselectivity of condensation of 3-methyl-1-phenyl-2-pyrazoline-4,5-dione with aromatic 1,2-diamines is dependent on substituent present. Isomeric 3-methyl-1-phenyl-1H-pyrazolo-[3,4-b]-quinoxaline products are distinguished by comparison of their 2D z-gradient selected 1H, 15N HMBC (Heteronuclear Multiple Bond Correlation) spectra. Multiplicity of H5 signal, which is recognizable by the cross-peak for CH3(3)-N4 and H5-N4 interactions, indicates substitution in position 6 or 7. The applied method is expected to be useful for structure determinations in other positional isomers.

Regioselective Synthesis of 2-Imino-1,3-thiazolidin-4-ones by Treatment ofN-(Anthracen-9-yl)-N′-ethylthiourea with Bromoacetic Acid Derivatives

2002

The reaction between N-(anthracen-9-yl)-N′-ethylthiourea (1) and methyl bromoacetate yielded mainly 2-[(anthracen-9-yl)imino]-3-ethyl-1,3-thiazolidin-4-one (2), together with some of the regioisomeric 3-(anthracen-9-yl)-2-ethylimino-1,3-thiazolidin-4-one (3). The structures of the products were elucidated by NMR techniques and, for 3, X-ray crystallographic analysis. Treatment of 1 with bromoacetyl bromide again yielded 2 and 3, but with a reversed product distribution ratio, thus providing an interesting and unexpected regioselectivity, depending on the electrophile selected. The underlying cause of the observed regioselectivity is a result of different reaction pathways taken by the two e…