Search results for " reaction"
showing 10 items of 4906 documents
Asymmetric Vinylogous Mannich-Type Addition of α,α-Dicyanoalkenes to α-Fluoroalkyl Sulfinyl Imines
2018
Abstract. The asymmetric vinylogous Mannich reaction (AVMR) of alfa,alfa-dicyanoalkenes with alfa-fluoroalkyl sulfinyl imines has been successfully accomplished. This transformation is unprecedented with fluorinated imines at the same time as the use of dicyanoalkenes in AVMR has been scarcely reported. Several fluorinated sulfinyl imines are compatible with the process, which gaves access to a family of chiral fluorinated amines with excellent level of stereocontrol. Interestingly, the selectivity found in our protocol is reverse to that encountered in analogous AVMR previously reported. Additionally, the synthetic applicability of the addition products has been exemplified with several tr…
Thiourea-Catalyzed Domino Michael–Mannich [3+2] Cycloadditions: A Strategy for the Asymmetric Synthesis of 3,3′-Pyrrolidinyl-dispirooxindoles
2017
The asymmetric synthesis of trifluoromethylated 3,3′-pyrrolidinyl-dispirooxindole derivatives with four contiguous stereogenic centers, including two vicinal spiro-stereocenters, is described. Employing a bifunctional thiourea catalyst, a domino Michael–Mannich [3+2] cycloaddition occurs readily between isatin ketimines and isatin-derived enoates with good yields and very high stereoselectivities, providing a direct entry to the title compounds of potential medical value.
Organocatalytic Asymmetric Synthesis of 2,3′-Connected Bis-Indolinones by Mannich Reactions of N-Acetylindolin-3-ones with Isatin N-Boc Ketimines
2017
A highly diastereo- and enantioselective Mannich reaction of N-acetylindolin-3-ones with isatin N-Boc ketimines to form 2,3′-connected bis-indolinones is developed employing a low loading of a readily available bifunctional thiourea catalyst. The asymmetric synthesis connects two indolinones via a vic-diamine unit and generates two neighboring stereocenters.
Catalytic enantioselective aza-Reformatsky reaction with seven-membered cyclic imines dibenzo[b,f][1,4]oxazepines
2017
A catalytic enantioselective aza-Reformatsky reaction is reported with cyclic dibenzo[b,f][1,4]oxazepines and ethyl iodoacetate leading to the synthesis of chiral ethyl 2-(10,11-dihydrodibenzo[b,f][1,4]oxazepin-11-yl)acetate derivatives with excellent yields and high enantioselectivities (up to 98% yield and 97 : 3 er) using a readily available diaryl prolinol L4 as the chiral ligand and Me2Zn as the zinc source under an air atmosphere. Furthermore, different transformations were carried out with the corresponding chiral β-amino esters, preserving in all cases the optical purity.
Cross-Metathesis/Intramolecular (Hetero-)Michael Addition: A Convenient Sequence for the Generation of Carbo- and Heterocycles
2017
The high stability and functional group compatibility of ruthenium carbene complexes confer them a great ability to catalyze domino processes. For this reason, the combination of metathesis reactions with additional transformations in a domino fashion has been exploited extensively, with the result of expanding the utility of ruthenium carbene complexes beyond that of just olefin metathesis. Among those domino processes, it is worth mentioning the sequence of cross-metathesis/intramolecular Michael addition, which allows for the generation of a wide variety of carbo- and heterocycles in a very simple manner, taking advantage of the benefits of domino reactions. Carbon-, oxygen- and nitrogen…
Molybdenum Pentachloride Mediated Synthesis of Spirocyclic Compounds by Intramolecular Oxidative Coupling
2015
The oxidative treatment of (m)ethyl 2-aryl cinnamates equipped with methoxy groups in position 4 of the phenyl moiety promote the formation of cyclohexadienone substructures. This dealkylative oxidative C–C coupling gives access to spirocyclic compounds and avoids the construction of the corresponding phenanthrenes. Furthermore, the transformation can be expanded to other spirocyclic systems.
Analysis of salivary detection of P16INK4A and RASSF1A promoter gene methylation and its association with oral squamous cell carcinoma in a Colombian…
2019
Background Epigenetic factors play a fundamental role in the etiopathogenesis of oral squamous cell carcinoma (OSCC). This study evaluated if salivary detection of P16INK4A/RASSF1A gene promoter methylation might be linked to the clinical/histological features of OSCC in a Colombian population. Material and Methods Methylation-specific polymerase chain reaction (MSP-PCR) was used to detect the methylation frequency of P16INK4A/RASSF1A genes in DNA obtained from whole saliva collected of 40 healthy controls (HC) and 43 OSCC patients. Determination of the clinical performance of MSP-PCR assay was based on standard algorithms derived from two-way contingency table analysis. The association of …
Quantitative models of hydrothermal fluid–mineral reaction: The Ischia case
2013
Abstract The intricate pathways of fluid–mineral reactions occurring underneath active hydrothermal systems are explored in this study by applying reaction path modelling to the Ischia case study. Ischia Island, in Southern Italy, hosts a well-developed and structurally complex hydrothermal system which, because of its heterogeneity in chemical and physical properties, is an ideal test sites for evaluating potentialities/limitations of quantitative geochemical models of hydrothermal reactions. We used the EQ3/6 software package, version 7.2b, to model reaction of infiltrating waters (mixtures of meteoric water and seawater in variable proportions) with Ischia’s reservoir rocks (the Mount Ep…
Phase Relations, Reaction Sequences and Petrochronology
2017
At the core of petrochronology is the relationship between geochronology and the petrological evolution of major mineral assemblages. The focus of this chapter is on outlining some of the available strategies to link inferred reaction sequences and microstructures in metamorphic rocks to the ages obtained from geochronology of accessory minerals and datable major minerals. Reaction sequences and mineral assemblages in metamorphic rocks are primarily a function of pressure ( P ), temperature ( T ) and bulk composition ( X ). Several of the major rock-forming minerals are particularly sensitive to changes in P–T (e.g., garnet, staurolite, biotite, plagioclase), but their direct geochronology …
2D Hydro-Mechanical-Chemical Modeling of (De)hydration Reactions in Deforming Heterogeneous Rock: The Periclase-Brucite Model Reaction
2020
Deformation at tectonic plate boundaries involves coupling between rock deformation, fluid flow, and metamorphic reactions, but quantifying this coupling is still elusive. We present a new two-dimensional hydro-mechanical-chemical numerical model and investigate the coupling between heterogeneous rock deformation and metamorphic (de)hydration reactions. We consider linear viscous compressible and power-law viscous shear deformation. Fluid flow follows Darcy's law with a Kozeny-Carman type permeability. We consider a closed isothermal system and the reversible (de)hydration reaction: periclase and water yields brucite. Fluid pressure within a circular or elliptical inclusion is initially bel…