Ionic Liquids in Heterocyclic Synthesis Martins, Marcos A. P; Frizzo, Clarissa P; Moreira, Dayse N ...
Chemical reviews,
06/2008, Letnik:
108, Številka:
6
Journal Article
Recenzirano
The effects of ionic liquids in cyclocondensation reactions are examined. The improvement in yield and shortening of reaction time due to these liquids can be explained by the theory of solvent ...effects.
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•Ultrasound is a powerful tool in the synthesis of pyrimidines.•Selectivity in the synthesis of pyrimidines under ultrasound is demonstrated.•Synergic effects of US combined with ...other methods are presented.
The pyrimidine scaffold is present in many bioactive drugs; therefore, efficient synthetic routes that provide shorter reaction times, higher yields, and site-selective reactions are constantly being sought. Ultrasound (US) irradiation has emerged as an alternative energy source in the synthesis of these heterocyclic scaffolds, and over the last ten years there has been a significant increase in the number of publications mentioning US in either the construction or derivatization of the pyrimidine core. This review presents a detailed summary (with 140 references) of the effects of US (synergic or not) on the construction and derivatization of the pyrimidine core through classical reactions (e.g., multicomponent, cyclocondensation, cycloaddition, and alkylation reactions). The main points that were taken into consideration are as follows: chemo- and regioselectivity issues, and the results of conventional heating methods compared to US and mechanistic insights that are also presented and discussed for key reactions.
This review describes advances in the synthesis of heterocyclic scaffolds (associated with their biological activity), using haloacetylated enol ethers as precursors. The wide variety of heterocycles ...that can be prepared using these precursors, together with the high regioselectivity they usually provide, in 3+2 and 3+3 cyclocondensation reactions, make these starting materials powerful tools. The biological evaluation is also highlighted, given that several analogues of commercially available drugs can be easily accessed.
Haloacetylated enol ethers are suitable starting materials for the regioselective synthesis of biologically relevant heterocyclic scaffolds. With this in mind, this review brings together advances in both synthetic and biological/pharmacological activities.
The crystallization mechanisms of a series of fourteen 7-chloro-4-substituted-quinolines (substituents: (
1
) OCH
3
, (
2
) OCH
2
CH
3
, (
3
) OCH
2
CH&z.dbd;CH
2
, (
4
) O(CH
2
)
2
OH, (
5
) O(CH
2
...)
3
OH, (
6
) NH(CH
2
)
2
CH
3
, (
7
) NH(CH
2
)
3
CH
3
, (
8
) NH(CH
2
)
2
OH, (
9
) NHCH(CH
2
CH
3
)CH
2
OH, (
10
) NH(CH
2
)
2
Cl, (
11
) NHN&z.dbd;CH(C
6
H
5
), (
12
) NHN&z.dbd;CH(2-FC
6
H
4
), (
13
) NHN&z.dbd;CH(3-FC
6
H
4
), and (
14
) NHN&z.dbd;CH(4-FC
6
H
4
)) were proposed based on a retrocrystallization approach using the supramolecular cluster as demarcation. Crystallization mechanism stage parameters -
N
CG
% and NG/NC - were determined. The 4-substituents present in quinolines caused six different mechanisms, starting from the monomers in solution to dimers, 1D nuclei, and 2D nuclei (
6
,
11
,
12
); 2D nucleus formation (
5
); 1D nuclei to 2D nuclei (
7
,
9
); concomitant dimers and 1D nuclei to a 3D crystal (
8
); 1D nuclei directly to a 3D crystal lattice (
1-4
,
10
,
14
), and dimers to 2D nuclei and then to a 3D crystal (
13
). Analysis of
G
AI
showed atom atom intermolecular interactions in the proposed first nuclei for compounds
4
and
5
. The nucleation process inferred in the solid state was partially confirmed during the formation of the proto-crystal in solution due to the changes of the hydrogen chemical shift in variable-concentration
1
H-NMR experiments. Results revealed that the size of the alkyl chain and the presence of different functional groups in the 4-substituents influenced the crystallization process.
The crystallization mechanisms of a series of fourteen 7-chloro-4-substituted-quinolines were proposed based on a retrocrystallization approach using the supramolecular cluster as demarcation.
Polymorphs have been widely studied since different crystalline phases of the same compound may have distinct properties. Macromolecules are an area of major study with just a few polymorphs ...reported. This investigation presents the first case of polymorphism in a 2rotaxane molecule. This rotaxane contains a succinamide station bearing nonsymmetric stoppers and a tetralactam macrocycle. A different polymorphic phase is achieved by varying the crystallization solvent. These polymorphs presented relevant differences at the molecular level and were classified as conformational polymorphs. At the supramolecular level, polymorph I is −21 kcal mol–1 more stable than polymorph II. Crystallization mechanisms to assess the stages of the crystallization process were proposed. Similar stabilization of the first nuclei formed was observed to be responsible for the possibility of both forms to coexist. The large differences observed between the polymorphs were not significantly reflected in the types and contribution of the intermolecular interactions, in which a high resemblance was observed.
The Wonderful World of β‐Enamino Diketones Chemistry Mittersteiner, Mateus; Andrade, Valquiria P.; Bonacorso, Helio G. ...
European journal of organic chemistry,
November 8, 2020, Letnik:
2020, Številka:
41
Journal Article
Recenzirano
The simple preparation and functionalization of oxa/aza heterocycles requires new and efficient starting materials to be discovered so that regioselective methodologies with a wide range of ...applications in organic synthesis can be developed. With this in mind, β‐enamino diketones have emerged as a suitable building block for preparing the most diverse (poly)heterocyclic systems, through cyclocondensation or cycloaddition reactions. This review compiles all the reactions that have been conducted using these starting materials, ever since they were first disclosed in 1980.
β‐Enamino diketones have risen as suitable starting materials for the construction of the most diverse classes of heterocycles through classical 3+2 and 3+3 cyclocondensation reactions with NN‐, NO‐ and NCN‐ dinucleophiles. This review gathers all reported works since its disclosure in the 80's and aspects like reactivity and selectivity are discussed thoroughly.
Deep eutectic solvents (DES) have been used as sustainable media for the synthesis of more efficient nanoparticle-based catalysts. However, the effects of DES deposition on the catalytic activity of ...metal oxide nanoparticles like TiO2 are unknown. Thus, the goal of this study was to facilitate the deposition of DES onto TiO2 surfaces and investigate how this coating modulates the catalytic activity of TiO2 in the photodecomposition of organic dyes. Results for the thermal and spectroscopic properties of the TiO2 coated with DES in relation to pure materials indicated interactions between these two materials, confirming the deposition of DES onto the TiO2 surface. Different choline chloride : HBD molar ratios had little impact on the thermal stability, phase transitions, crystallization and amorphization of the mixture. In general, the catalytic activity of TiO2 coated with DES was reduced. However, TiO2 covered with ChCl : malonic acid (1 : 2) showed the best catalytic activity and it was better as greater the amount of DES used in the surface deposition.
The selective N- or O-alkylation of 4-(trihalomethyl)pyrimidin-2(1H)-ones, using 5-bromo enones/enaminones as alkylating agents, is reported. It was found that the selectivity toward the N- or ...O-regioisomer is driven by the substituent present at the 6-position of the pyrimidine ring, thus enabling the preparation of each isomer as the sole product, in 60–95% yields. Subsequent cyclocondensation of the enaminone moiety with nitrogen dinucleophiles led to pyrimidine–azole conjugates in 55–83% yields.
A mild and efficient protocol for the assembly of tetra-substituted 5-trifluoromethylpyrazoles is presented, involving halogenation at the 4-position of readily prepared tri-substituted ...5-trifluoromethylpyrazoles to give 4-halo-1-phenyl-5-trifluoromethyl pyrazoles, and subsequent palladium-catalyzed Negishi or Buchwald-Hartwig cross-couplings to install carbon or nitrogen-based 4-substituents. Key to the success of these challenging cross-couplings is the use of XPhos and JosiPhos CyPF-tBu ligands, respectively.
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