Guillermo Penieres

Unusual Oxidative Dealkylation of Certain 4-Alkyl-1,4-Dihydropyridines With MnO2/Bentonite Using Microwave Irradiation, in the Absence of Solvent (II)

Abstract Several Hantzsch 4-alkyl-1,4- dihydropyridines have been oxidized to the corresponding aromatic systems. An unexpected mixture of 4-alkyl pyridines and/or dealkylated pyridines are formed.

MODIFICATION OF THE FISCHER INDOLE SYNTHESIS.

We describe a novel modification of the Fischer indole synthesis by using a natural clay and infrared irradiation. Introduction. Primarily, because of their pharmacological importance, heterocyclic compounds have been the subject of considerable synthetic activity during the past several years. For this reason, indoles have attracted much attention. There are general methods described so far for the preparation of indoles involving different reagents. The Fischer reaction(1) is a common synthetic method used to obtain these compounds which involves heating a phenylhydrazone in presence of an acid catalyst, e.g.: ZnCI2, BF3 (1)r PCI3 (2) or polyphosphoric acid (3). The product yield and the success of the Fischer indole synthesis depends largely upon the choice of catalyst and the reaction conditions. The effectiveness of different materials such as hydrogen chloride, hydrochloric acid and varying proportions of ZnCl2 in catalyzing the indolization of acetone 4-chlorophenylhydrazone has been investigated (4) Another old modification, known as the Fischer-Arbuzow reaction (5), employs catalytic amounts of the Lewis acid. On the other hand, a bentonitic earth (an aluminosilicate) has been used in several organic reactions as catalyst or reagent support, yielding good results (6-8). The physical and chemical properties of the clay were previously reported (9). Continuing our research on the use of a natural bentonite as a Lewis acid catalyst, we have now developed a modified Fischer procedure using infrared energy as a convenient method to obtain indole derivatives. Experimental. In a general experiment 1 mmol of Phenylhydrazine and 1 mmol of ketone were mixed with 4g of clay and the mixture was IR irradiated with a commercial lamp of 250 W for 30 min. Then, the product was extracted with ethanol, the clay was eliminated by filtering and the solvent evaporated under vacuum. The resulting compound was purified by recrystalization with a 1:1 ethanol-water mixture and spectroscopically identified by IR with a Perkin Elmer Model 283 spectrophotometer, H NMR using a Varian FT-200 spectrometer, and MS with a Hewlett Packard Model 5890. Results and Discussion. The results of several experiments are summarized in Table 1.

A NEW STRATEGY FOR THE SYNTHESIS OF N-SUBSTITUTED 2,5-DIMETHYLPYRROLES IN HETEROGENEOUS MEDIUM.

A novel preparation in dry medium of N-substituted 2,5-dimethylpyrroles using a clay as catalyst and infrared energy is described. Introduction. It is well know that the Paal-Knorr reaction is the most general synthetic method to prepare furan, pyrrole and thiophene derivatives (1). This method consists in the reaction of a 1,4-dicarbonyl compound with a dehydrating acid, or ammonia, primary amines, hydroxylamine, hydrazines or an inorganic sulfur salt, respectively. An interesting application of this method is the protection of a primary amine group against attack by strong bases or nucleophiles by incorporation into an N-substituted 2,5-dimethylpyrrole system from which the amine group is regenerated by treatment with hydroxylamine hydrochloride (2). In previous papers, we described the use of a natural clay as acid catalyst in different organic reactions (3-6). We present in this report the results obtained for the reaction of primary amines with acetonylacetone using infrared radiation and a natural clay as catalyst in absence of solvent, as a variation to the Paal-Knorr reaction. Results and Discussion. Several N-substituted 2,5-dimethylpyrroles were obtained by the proposed method (Table 1). Because of the short reaction times and the high yield of the obtained products, we believe that this new method can be considered as a simple, efficient and good alternative general route to generate the titled compounds. We observed that when the reactions were repeated following the general procedure without the use of the clay, in the majority of the cases the reaction product was not formed, and only in the case of p-methylaniline and benzylamine was the pyrrole derivative formed and in low yield (minor to 20%) and with longer reaction times (more than 30 minutes). Then, the catalyst provides more desireable conditions to this modification for the Paal-Knorr reaction. Furthermore, we hope that this method can be implemented to synthesize homologue structures with other heteroatoms. Vol. 4, No. 1, 1998 A New Strategy For The Synthesis of N-substituted, 2,5 Dimethylpyrroles in Heterogenous Medium Table 1. Synthesis of N-Substituted 2,5-Dimethylpyrroles

COMPARATIVE STUDY OF ε-CAPROLACTAM SYNTHESIS USING DIFFERENT ENERGY SOURCES AND A NATURAL CLAY AS CATALYST

We report a new method for the production of ε-caprolactam from cyclohexanone and NH2OH.HCI using different sources of energy in presence of a Mexican clay in dry medium. Introduction. One of the classical reactions in organic chemistry is the Beckmann rearrangement (1). An important industrial application of this process is in the synthesis of ε-caprolactam, which is the raw material for obtaining Nylon 6. Recently, this lactam has been prepared by the Beckmann reaction of cyclohexanone oxime and using a zeolite as catalyst (2), or by refluxing a suspension of 6-aminocaproic acid previously supported in zeolite, silica gel or alumina (3). We have reported previously the use of a natural clay as acid catalyst in several organic reactions, such as the regeneration of carbonyl compounds from their oxime derivatives (4,5). In the case of p-hydroxy and p-methoxy acetophenone oximes; the carbonyl compound was not regenerated, but the corresponding amides were obtained through the Beckmann rearrangement. This observation and the fact that oximes can be prepared in dry medium (6), led us to consider the transformation reaction of aromatic aldehydes into the corresponding nitriles in a one step reaction. Also in this case the Beckmann rearrangement was observed. We present here, the results of a comparative study for the synthesis of εcaprolactaim when cyclohexanone and NH2OHOHCI are irradiated with infrared, ultrasound, microwave or heat as energy sources using a natural clay (Table 1). Results and Discussion. Table 1 shows that when weak bases, such as Na2C03 or NaHC03 are used, the yield of ε-caprolactam increases in all but one case (ultrasound). The best conversion (92%) was obtained with infrared radiation. Although the acid character of the natural clay satisfy the conditions required for the Beckmann rearrangement, in earlier experiments using more acidic conditions, we found that the caprolactam yield was near zero with microwave energy. Therefore, we decided to add weak basic compounds to the reaction mixture and found surprisingly that the yields increased dramatically when infrared or microwave radiation was used. We suggest, in accord with Sato and coworkers (2), that the active site in the catalyst is a neutral moiety; hence, the role of base is thought to be to neutralize the hydroxyl amine hydrochloride so the free hydroxyl amine could undergo nucleophillic attack on the cyclohexanone. We propose that the oxime is formed as an intermediate and it can give the Beckmann rearrangement or carbonyl compound regeneration. This behavior is clearly observed when infrared, microwave and thermal energy were used. However, when ultrasound energy was used, the oxime was one of the main reaction products.

One Pot Syntheses of Substituted Naphthyridines and 2H-Pyrano[3,2-g]-quinolin-2-ones in Water

One pot catalytic syntheses of substituted 1,8-naphthyridines and 2H-pyrano[3,2-g]quinolin-2-ones by the reaction of α-ketoalkynes with 6-aminonicotinamide and 7-amino-4-methylcoumarin respectively in water, using a homogeneous nickel catalyst at very mild reaction conditions are described. In the absence of this catalytic system very low yields are obtained even after long reaction time.

Allylic nitration of 3β-sitosterol and cholesterol acetate: Preparation of 7-nitro derivatives

The reaction of 3-β-sitosterol and cholesterol acetates with a HNO3/bentonite system using infrared or microwave radiation as the energy source leads to 7-nitro derivatives as major products.

Theoretical Characterization of Three 2,2-Diphenyl-1,3,2-oxazaborolidin-5-ones: Molecules with Fungicide Activities

In this study, a theoretical characterization for three 2,2-diphenyl-1,3,2-oxazaborolidin-5-ones was performed using Density Functional Theory. The analyzed molecules have antifungal activity, making them of particular interest.

Synthesis of novel dinuclear complexes of Fe(O) derived from 1,2-dicarbonylic monohydrazones

Abstract Synthesis of three novel dinuclear complexes of Fe(O) are reported, la-c were prepared by-reaction of the corresponding monohydrazones with Fe2(CO)9. The structures of the complexes were determined by IR, 1H and 13C-NMR and HR-MS.

ANTIMONY TRICHLORIDE MEDIATED TRIMERIZATION OF BENZOTHIAZOLE: CRYSTAL STRUCTURE OF 2,2-BIS[BENZOTHIAZOLYL]BENZOTHIAZOLE.

The reaction of three equivalents of antimony trichloride with 2-lithium benzothiazole leads to a trimeric, coupling product. This reaction is similar to those in which PCI3 leads to heterocycle dimerization. The monomeric, molecular structure of the title compound was determined by X-ray crystallography. The crystal is monoclinic, a=14.681(1) A, b=8.491(2) A, c=15.966(6) Α, ß=108.00(2)°; space group P2,/n, Z=4 for C2iH13N3S3, and Pcaicd=1-416 g/cm.