Francisco Delgado

Knoevenagel Condensation in Heterogeneous phase Catalyzed by IR Radiation and Tonsil Actisil FF

Abstract Infrared radiation promoted the synthesis of benzylidenemalononitriles, benzylidenecyanoacetamides and benzylidenecyanoacetic acids by condensation of aromatic aldehydes with the corresponding active methylene compound in the presence of Tonsil Actisil FF, without solvent. Mass of catalyst, solvent, and reaction time were assessed in order to improve the efficiency of this process.

Preparation of Benzylidene Barbituric Acids Promoted by Infrared Irradiation in Absence of Solvent

Abstract Several benzaldehydes were condensed with barbituric acid under infrared irradiation, in absence of solvent, affording the corresponding 5-benzylidene barbituric acids.

Knoevenagel Condensation Catalyzed by a Mexican Bentonite Using Infrared Irradiation

Abstract Diethyl malonate undergoes condensation with aromatic aldehydes without solvents. in the presence of a Mexican bentonite using infrared irradiation as the energy source, to give the benzylidenemalonate compounds in fair yield.

Infrared irradiation: Effective promoter in the formation of N-benzylideneanilines in the absence of solvent

Abstract Infrared irradiation promoted the formation of a series of Schiff bases in the condensation reaction between benzaldehydes and anilines, in the absence of solvent. Benzaldehydes and anilines, containing either electron‐withdrawing or electron‐releasing groups, were assessed to identify any substituent effect on the formation of the Schiff bases. This methodology is characterized by ease of set‐up and work‐up, and the reaction yields were comparable with those obtained in the methods reported previously. Moreover, this new procedure is environmentally benign because no solvent was employed in the transformations.

Characterization of a bentonitic clay and its application as catalyst in the preparation of benzyltoluenes and oligotoluenes

Abstract The preparation of oligomeric toluenes catalyzed with a bentonitic clay, using thermal energy and ultrasound, was performed and evaluated. When ortho and para benzyltoluenes were studied, the oligomerization reaction was found to be dependent of the catalyst amount, reaction time, temperature and the presence of pyridine as competitive inhibitor. A proposal for the molecular structure calculation analysis at semiempirical AM1 level was proposed based on the regioselectivity and in the oligomerization pathway. Furthermore, a detailed study to characterize the clay was performed, thus several physicochemical properties of the clay were determinated by means of: 29 Si and 27 Al MAS–NMR, X-ray diffraction, X-ray fluorescence, scanning electron microscopy, IR spectrophotometry, thermal analysis (DTA, TG-DTG), and adsorption techniques (N 2 -BET).

Regioselective synthesis of 1,2-dihydroquinolines by a solvent-free MgBr2-catalyzed multicomponent reaction.

A highly efficient and regioselective synthesis of 1,2-dihydroquinolines via a multicomponent reaction between an aniline and two ketones is described. This reaction was catalyzed by magnesium bromide and carried out under solvent-free conditions. When the reaction was performed by using 3-substituted anilines and nonsymmetrically substituted ketones, principally a single product was found among the four expected regioisomers. A variety of anilines and ketones, including cyclic ketones, were evaluated providing a series of 1,2-dihydroquinolines with diverse substitution patterns. A study of the mechanism is discussed. There is evidence of the in situ formation of the imine as a result of the reaction between the aniline and one of the ketones, before annulation to the heterocyclic ring.

Highly Regio- and Stereoselective Diels-Alder Cycloadditions via Two-Step and Multicomponent Reactions Promoted by Infrared Irradiation under Solvent-Free Conditions

Infrared irradiation promoted the Diels-Alder cycloadditions of exo-2-oxazolidinone dienes 1–3 with the Knoevenagel adducts 4–6, as dienophiles, leading to the synthesis of new 3,5-diphenyltetrahydrobenzo[d]oxazol-2-one derivatives (7, 9, 11 and 13–17), under solvent-free conditions. These cycloadditions were performed with good regio- and stereoselectivity, favoring the para-endo cycloadducts. We also evaluated the one-pot three-component reaction of active methylene compounds 20, benzaldehydes 21 and exo-2-oxazolidinone diene 2 under the same reaction conditions. A cascade Knoevenagel condensation/Diels-Alder cycloaddition reaction was observed, resulting in the final adducts 13–16 in similar yields. These procedures are environmentally benign, because no solvent and no catalyst were employed in these processes. The regioselectivity of these reactions was rationalized by Frontier Molecular Orbital (FMO) calculations.

Synthesis and highly selective Diels–Alder cycloadditions of the new dienes N-substituted 2,3,5,6-tetrahydrobenzoxazol-2-ones

Abstract The synthesis of the new dienes N -substituted 2,3,4,5-tetrahydrobenzoxazol-2-ones 8a – 8c is described, through a one-step convergent process from 1,2-cyclohexanedione ( 7a ) and the corresponding isocyanates 2a – 2c . The presence of electron-donor substituents in the aryl ring of the isocyanate gave rise to the exclusive formation of the captodative olefins 10 . Diene 8a proved to be reactive and stereoselective in Diels–Alder additions with a cyclic olefin. The reaction with acetylenic dienophiles yielded the 2,3-dihydrobenzoxazol-2-ones 21 and 24 , as the products of sequential [4+2] cycloaddition and retro-Diels–Alder reactions. Methyl vinyl ketone ( 22 ) underwent regio- and stereoselective tandem Diels–Alder and Michael additions to give propellane 29a . Evidence of an endo π-pyramidalization of the central double bond of adduct 19 would rationalize the exo stereoselection in the formation of 29a . The regioselectivity in these reactions has been rationalized in terms of FMO theory by ab initio calculations.

Vasodilator Effects of Bis-Dihydropyridines Structurally Related to Nifedipine

Calcium channel blockers are widely used in therapy for hypertension and angina pectoris, and among these blockers some 1,4-dihydropyridines (e.g. amlodipine, nitrendipine and nifedipine) have had widespread clinical use. In this work we investigated the vascular effects of four bis-1,4-dihydropyridines (bis-DHPs: 01-04), structurally related to nifedipine, in which a second 1,4-dihydropyridinic moiety was incorporated in the corresponding arylic moiety in para and meta position. Of these four bis-DHPs, the meta regioisomers (bis-DHP-03 and bis-DHP-04; 0.01-3.16 mg kg(-1)) and nifedipine induced a greater decrease on diastolic and systolic blood pressure than the para isomers (bis-DHP-01 and bis-DHP-02), as shown in two experimental models: normotensive and spontaneously hypertensive rats. Complementarily, bis-DHPs action was examined in intact and endothelium-denuded rat aorta, depolarized by KCl [80 mM] in one group and stimulated by noradrenaline (1 x 10(-7) M) in another and the corresponding IC(50) values were obtained (1.5 x 10(-6)-2. 4 x 10(-7)M). Later, the relaxing action of bis-DHP-03,04 and nifedipine on the contraction evoked by Ca(2+) in K(+)-depolarized rat aorta was analyzed and the corresponding EC(50) values for the meta isomers and nifedipine were obtained. The results showed a concentration dependent vasodilating activity in both KCl precontracted and noradrenaline stimulated aorta rings. The apparent order of potency with and without endothelium in both experimental models was nifedipine >bis-DHP-04 >bis-DHP-03. The cumulative concentration-effect curves for Ca(2+) in the presence of the bis-DHPs tested show the same potency order. Unlike nifedipine, the tested compounds are not photosensitive, which makes them more attractive in therapy for hypertension related diseases.

Captodative olefin 3-p-nitrobenzoyloxy-3-buten-2-one asa diels-alder ketene equivalent for the synthesisof γ-hydroxycyclohexenones

Abstract A short and regioselective synthesis of γ-hydroxycyclohexenones is described, using 3- p -nitrobenzoyloxy-3-buten-2-one ( 2a ) as a ketene equivalent in Diels-Alder reactions with substituted dienes. Oxidation with MCPBA of the α-acetylcyclohexenol derivative, obtained by hydrolysis of the cycloadducts, led to the corresponding γ-hydroxycyclohexenones in moderate overall yields. Evidence of the mechanism is provided.