Search results for "REGIOSELECTIVITY"
showing 10 items of 298 documents
ChemInform Abstract: Unique Regioselectivity in the C(sp3)-H α-Alkylation of Amines: The Benzoxazole Moiety as a Removable Directing Group.
2015
The benzoxazol-2-yl substituent is easily introduced by oxidative coupling or nucleophilic substitution and can be removed by hydroxide or by hydride reduction.
A DFT study of the [3 + 2] versus [4 + 2] cycloaddition reactions of 1,5,6-trimethylpyrazinium-3-olate with methyl methacrylate.
2013
The reaction between 1,5,6-trimethylpyrazinium-3-olate and methyl methacrylate (MMA) yielding a lactone-lactam has been studied using the DFT method at the B3LYP/6-31G(d) level. It is concluded that formation of the lactone-lactam is a domino process involving three consecutive reactions: (i) a 1,3-dipolar cycloaddition (13DC) reaction between the pyrazinium-3-olate and MMA yielding a [3 + 2] cycloadduct (CA); (ii) a skeletal rearrangement, which converts the [3 + 2] CA into a formal [4 + 2] CA, possessing a diazabicyclo[2.2.2]octane structure; and finally, (iii) an S(N)2 reaction, promoted by halide anion, with concomitant nucleophilic attack of the created carboxylate anion on an iminium …
ChemInform Abstract: Modular One-Pot Synthesis of Tetrasubstituted Pyrroles from α-(Alkylideneamino)nitriles.
2008
2,3,4,5-Tetrasubstituted pyrroles have been prepared with high regioselectivity by a formal cycloaddition of α-(alkylideneamino)nitriles and nitroolefins followed by elimination of HCN and HNO2. The reaction allows the convergent construction of the pyrrole ring in four steps from a nitroalkane and three aldehydes.
A new method for the regioselective synthesis of β-enamino acid derivatives
1993
Abstract A mild, simple and efficient route to β-enamino imidazole carbonilic derivatives 3 by reaction of ketimines with N,N′ -carbonyl diimidazole in the presence of boron triflouride as catalyst has been developed. The conversion of 3 to esters has also been explored.
Influence of Reactant Polarity on the Course of the Inverse-Electron-Demand Diels−Alder Reaction. A DFT Study of Regio- and Stereoselectivity, Presen…
1999
The molecular mechanisms for the inverse-electron-demand Diels−Alder reactions between nitroethene and three substituted ethenes (propene, methyl vinyl ether, and dimethylvinylamine) to give the corresponding nitroso cycloadducts have been characterized with density functional theory methods using the B3LYP/6-31G* calculational level. On the basis of stability arguments and molecular orbital analysis relative rates, regioselectivity, and stereoselectivity, the presence of Lewis acid catalyst modeled by the BH3 system and the inclusion of solvent effects as a function of the nature of substituent in the dienophile fragment are analyzed and discussed. The ortho attack mode presents transition…
ChemInform Abstract: Triazolopyridines. Part 26. The Preparation of Novel [1,2,3]Triazolo[1,5-a]pyridine Sulfoxides.
2008
Abstract The regioselective synthesis of new triazolopyridine halides and sulfoxides with the substituent in all different ring positions of [1,2,3]triazolo[1,5- a ]pyridines is presented. The triazolo ring opening reaction of some representative sulfoxides to obtain disubstituted pyridines is also studied.
ChemInform Abstract: A New Method for the Regioselective Synthesis of β-Enamino Acid Derivatives.
2010
Abstract A mild, simple and efficient route to β-enamino imidazole carbonilic derivatives 3 by reaction of ketimines with N,N′ -carbonyl diimidazole in the presence of boron triflouride as catalyst has been developed. The conversion of 3 to esters has also been explored.
ChemInform Abstract: Reactivity and Selectivity of ortho-Metalated Rhodium(II) Complexes in C-H Insertion Reactions of α-Diazo Compounds.
2010
Regioselective intramolecular C−H insertion reactions of α-diazo β-keto esters and α-diazo ketones are mediated by Rh2[OOCR]4-x[PC]x (x = 1, 2; PC = ortho-metalated phosphine; R = CH3, C3F7). In particular, the intramolecular transformation of 1-diazo-5-methyl-3-propyl-2-hexanone catalyzed by Rh2[OOCCH3]2[PC]2 (PC = (C6H4)P(C6H5)2, head-to-tail (H−T) configuration) afforded only the tertiary C−H insertion product. By comparison, no C−H insertion reaction was promoted by doubly metalated complexes with a head-to-head (H−H) configuration. Rh2[OOCR]3[PC] compounds were found to be less suited for these type of reactions.
Triazolopyridines. Part 26: The preparation of novel [1,2,3]triazolo[1,5-a]pyridine sulfoxides
2008
Abstract The regioselective synthesis of new triazolopyridine halides and sulfoxides with the substituent in all different ring positions of [1,2,3]triazolo[1,5- a ]pyridines is presented. The triazolo ring opening reaction of some representative sulfoxides to obtain disubstituted pyridines is also studied.
A combined experimental and theoretical study of the alkylation of 3,5-dithioxo-[1,2,4]triazepines
2008
The chemo- and regioselective alkylation reactions of 3,5-dithioxo[1,2,4]triazepine 1 in a basic medium with α,ω-dibromoalkanes 2a–c, Br(CH2)nBr (n = 1–3), are studied experimentally and theoretically. These alkylations, which occur at the thioxo sulfur atom in position 5, afford mainly 5-bromomethylthio-2,7-dimethyl- 2,3-dihydro- 4H[1,2,4]triazepin-3-one 3 for n = 1, 6,8-dimethyl-5-thioxo-2,3,4,5-tetrahydro-6H[1,3]thiazolo[4,5-d][1,2,4]triazepine 4 for n = 2 and 7,9-dimethyl-6-thioxo-2,3,4,5,6,7-hexahydro[1,3]thiazino [4,5-d][1,2,4]triazepine 5 for n = 3. Theoretical calculations have been carried out at the B3LYP/6-31G* and B3LYP(benzene)/6-311+G*//B3LYP/6-31G* levels, in order to rationa…