Ahmed M. El-Khawaga

Synthesis of Some Pyridothienopyrazolopyrimidopyrimidine and Mercaptomethylpyrazolopyrimidine Derivatives

Mercaptomethylpyrazolopyrimidine (2) was synthesized and reacted with ethyl chloroacetate to afford ethyl pyrazolpyrimidinylmethylmercapto acetate ( 3) , which in turn was converted into the corresponding carbohydrazide 4 . Carbohydrazide 4 reacts with a variety of reagents to give different pyrazolopyrimidines ( 5–12 ). Chloromethyl-pyrazolopyrimidine (1) reacts with chloropyridine to give compound 13 , which was subjected in a series of reactions to give new compounds 14–20 .

Modern Friedel-Crafts chemistry. XI: Cyclization of aryl haloalkyl sulfones, arylsulfonylacyl chlorides and their corresponding sulfides

Abstract The sulfone group deactivation for cyclialkylation and cycliacylation reactions in the presence of Friedel-Crafts catalysts was demonstrated in a number of aryl chlorlalkylsulfones (1–8) and arylsulfonylacyl chlorides (17a-22a), respectively. As expected, the corresponding arylchloralkyl sulfides (9–16) and arylmercaptoacyl chlorides (13a-28a) underwent ring-closure reaction in most cases under the same conditions. The ease of cyclization was governed by the ring size, the stability of the attacking carbocation and the nucleophilicity of the aryl moiety. Also the behaviour of benzyl sulfones (29, 31a, and 32a) and sulfides (33, and 36a) was inconsistent. Noteworthy, the Friedel-Crafts cyclization reaction is thus considered an accessible method for the synthesis of compound 37–41 and 45,51.

SYNTHESIS AND REACTIONS OF SOME ISOQUINOLINE DERIVATIVES

Abstract Treatment of 3,4-tetramethylene-6-amino-5-cyano-thiopyran-2(1H)thione (1) with alkali followed by acidification with HCl afforded 1,2,5,6,7,8-hexahydro-4-cyano-3(2H)-oxoisoquinoline-1-thiol (2). When compound (1) was reacted with excess alkyl halides the corresponding O- and S-alkylated isoquinolines (3) were obtained. Also, α-chloroacetic acid and β-bromopropionic acid reacted with compound (2) to produce thiazolo and thiazinoisoquinoiines (4) and (5). Furthermore, the reaction of (2) with one mole of phenacylbromide produced-S-phenacyl derivatives (6), which cyclized to give the corresponding thiazoloisoquinoline (7). However two moles of phenacyl bromides gave the corresponding S- and O-phenacyl derivatives (8). The later compounds were cyclized to give furoisoquinoline derivative (9).

Liquid crystalline polymers XII. Main chain thermotropic poly(arylidene-ether)s containing 4-tertiary-butyl-cyclohexanone moiety linked with polymethylene spacers

A new homologous series of thermotropic liquid crystalline (LC) poly(arylidene−ether)s based on 4-methyl cyclohexanone moiety was synthesised by solution polycondensation of 4,4′-diformyl-α,ω-diphenoxyalkanes, Ia−f or 4,4′-diformyl−2,2′-dimethoxy-α,ω-diphenoxyalkanes IIa−f with the 4-methyl-cyclohexanone monomer. A model compound was synthesised from the monomer with benzaldehyde and characterised by elemental and spectral analyses. The inherent viscosities of the resulting polymers were in the range of 0.02−0.36 dI/g. All the poly(arylidene−ether)s were insoluble in common organic solvents and partially soluble in halogenated solvents. The mesomorphic properties of these polymers were studied as a function of the diphenoxyalkane spacer length. Their thermotropic LC properties were examined by differential scanning calorimetry (DSC) and optical polarising microscopy, and it was demonstrated that the resulting polymers form nematic mesophases over wide temperature ranges. The thermogravimetric analyses of those polymers were evaluated by thermogravimetric analysis and DSC measurements and correlated to their structural units. X-ray analysis showed that polymers have some degree of crystallinity in the region 2θ = 5−60°. In addition, the morphological properties of selected examples were tested by scanning electron microscopy.

NONCONVENTIONAL FRIEDEL-CRAFTS CHEMISTRY II. ON THE CATALYTIC ACTION OF TRIFLIC ACID AND ALUMINIUM CHLORIDE ON SELECTED ARYL THIOESTERS

Abstract The catalytic action of triflic acid and/or aluminium chloride on seven selected aryl thioesters (1-7) gave in all cases aryl thiols, diaryl sulfides, diaryl disulfide, and thianthrene derivatives in addition to the corresponding aryl carboxylic acids. Thioester 5 gave thiochromanone derivatives in good yield under the same conditions. Plausible mechanisms were suggested to rationalize the obtained results.

MOLECULAR REARRANGEMENTS. VI. THERMOLYSIS OF α-(N-ARYL)BENZYL ARYL SULFIDES

Abstract In view of the significance of studying the effect of heat on organic compounds especially those containing nitrogen and/or sulfur, six substituted α-(N-aryl) benzyl aryl sulfides (4–9) were prepared and subjected to thermolysis at 200°C. Surveying of the reaction products showed the formation of amines, benzylidene amines, sulfides, disulfides, dibenzyl, stilbene, benzthiazole, benzimidazole, tetraphenyl thiophene as principle products in variable ratios according to the type of the starting sulfide. A mechanism involving the homolytic cleavage of the C[sbnd]S and the C[sbnd]N bond is suggested to rationalize the thermolysis products.

CYCLIZATION OF SELECTED BENZYL SULFONE DERIVATIVES UNDER PHASE TRANSFER CATALYTIC CONDITIONS

Abstract Seven selected benzyl chloroalkyl sulfones(1a-c) and benzyl carboethoxyalkyl sulfones (1d-q) has been subjected to treatment with aqueous NaOH (50%) under PTC conditions. Analysis of the product mixtures revealed competitive cyclization, elimination and hydrolysis reactions. Correlation of the reaction products and the starting sulfone has been discussed.

MODERN FRIEDEL-CRAFTS CHEMISTRY XVI. REACTION OF THIOPHENE WITH BIFUNCTIONAL MOLECULES UNDER DIFFERENT FRIEDEL-CRAFTS CATALYSTS: ATTEMPTED SYNTHESIS OF CYCLOPENTA[b] THIOPHENES AND DIHYDROBENZO[b] THIOPHENES

Abstract The reaction of thiophene (1) with 3-chloropropionyl chloride (2), 4-chlorobutyryl chloride (3), crotonyl chloride (4) and cinnamoyl chloride (5) under different Friedel-Crafts catalysts (A1C13/CH3NO2, FeCl3, and A1C13/CS2) was investigated. The cyclic products 4,5-dihydro-6H-4-methylcyclo-pental[b]-thiophen-6-one, 5,6-dihydrobenzo[b]thiophen-7(4H) one and 4-phenyl-6H-cyclopenta[b]thio-phen-6-one were formed. The different behaviors of compounds (2–5) towards thiophene were discussed.

Modern Friedel-Crafts chemistry. XIV: On the cyclization of selected aryl hydroxyalkyl sulfides

Abstract The feasibility of cycloalkylation reactions in the presence of Friedel–Crafts catalysts was demonstrated in a number of aryl hydroxyalkyl sulfides (1–5), and benzyl hydroxyalkyl sulfides (6–7). Treatment of compounds (1–7) with Friedel-Crafts catalysts gave diaryl disulfides, diaryl sulfides, arene thiols, chlorohydrins, aryl chloroalkyl sulfides, aryl alkenyl sulfides and cyclization products. It is noteworthy to mention that cyclization products were isolated only in cases where the hydroxyl group is linked to a tertiary carbon atom as in compounds 3 and 7. A suitable reaction pathway is suggested to rationalize the formation of the various reaction products.

Elimination of thiophenol from phenyl orthothioesters in the mass spectrometer and novel rearrangement of ketene thioacetals upon electron impact

Abstract The mass spectra of four selected phenyl orthothioesters (1–4) have been measured. The obtained spectra revealed the conversion of the compounds (1–4) into ketene thioacetals (5–8) via the elimination of thiophenol in the mass spectrometer. The thermal nature of the process was confirmed and the mass spectra of ketene thioacetals (5–8) have been discussed. A novel fragmentation path for ketene thioacetals was suggested.