El Sayed Ramadan

Condensed 1,2,4-triazines. I: Fused to heterocycles with three-, four-, and five-membered rings

Publisher Summary Compounds containing the 1,2,4-triazine moieties are largely used as pharmaceuticals, dyes, pesticides, and herbicides. Great interest is directed to the synthesis of the title heterocycles having potentially useful biological properties. A large number of 1,2,4-triazines that are condensed with one or more heterocycles are well known and a wide variety of synthetic methods for their preparations are available. This chapter illustrates the triazines that are fused to heterocycles with three, four, and five-membered rings. It covers the survey of the literature of these condensed compounds from 1974 to 1992. The parent compound of this series has two Kekule structures. It can be fused with other heterocycles at its six different sites. The 1,2,4-triazine ring can also constitute a central unit in a condensed ring system, where two or more faces are included in fusions. It is noted that the heterocycles having fused benzene rings are categorized according to the heterocycle that is directly fused to the triazine ring.

Microwave Irradiation for Accelerating Organic Reactions. Part I: Three-, Four- and Five-Membered Heterocycles

Publisher Summary The microwave (MW) region of the electromagnetic spectrum lies at frequencies from 0.3 to 300 GHz. The energy transitions in the MW region are enough to cause bond rotation. Recently, microwave irradiation (MWI) has attracted much attention as a tool of preference in achieving and/or accelerating organic reactions. When matter is irradiated with MW, the ability of a molecule to absorb MWI is a function of two main mechanisms. These are namely molecular polarizability which in turn is a function of its dipole moment, and its ionic conduction. This chapter reviews the literature on the synthesis and reactions of three-, four- and five-membered heterocycles using MWI. It is divided according to the order of increasing size of the heterocycles and the number of heteroatoms. Each type is described according to their methods of preparation of the desired ring and by their reactions. Heterocycles having fused benzene rings have also been discussed.

Microwave‐Assisted Synthesis of Quinoline Derivatives from Isatin

Abstract Microwave irradiation has been used for a rapid and efficient synthesis of quinoline‐4‐carboxylic acids 5a–g and 1,2,3,4‐tetrahydroacridine‐9‐carboxylic acid (6) from the reaction of isatins 1–3 with acyclic and cyclic ketones in basic medium. 2‐Hydroxyquinoline‐4‐carboxylic acid (11) was also obtained by irradiating a mixture of isatin 1 and malonic acid in AcOH. The esters of 5f and 11 and their respective hydrazides 8 and 13 were also prepared under MWI.

Condensed 1,2,4-Triazines: II. Fused to Heterocycles with Six- and Seven-Membered Rings and Fused to Two Heterocyclic Rings

Publisher Summary This chapter deals with condensed ring systems of 1,2,4-triazines with six and seven-membered heterocycles, and condensed ring systems with triazine in the center. The chapter considers the order of increasing number of heteroatoms in the fused ring and each is followed in turn by a heterocycle fused to a benzene ring. Each fused ring system is arrangedaccording to the order of fusion on the triazine ring. Specifically, the chapter describes pyrido[1 ,2,4]triazines, pyrano[ 1 ,2,4]triazines, diazino[1,2,4]triazines, [ 1 ,2,4]triazino-oxazines, [ 1 ,2,4]triazino-thiazines, triazino[ 1 ,2,4]triazines, triazino-oxadiazine, triazino-thiadiazine, triazino-dioxazines, and heterocyclo-triazino heterocycles. With regard to pyrido[l,2,4]triazines, it is observed that there are eight theoretically possible pyridotriazines. Four of them possess bridgehead nitrogen with faces b , c , d , and f common to the triazine ring. The other four isomers have face e in common. Their UV spectral properties are generally dependent on the position of the pyrido N -atom.

Synthesis of Aryloxyacetic Acids, Esters, and Hydrazides Assisted by Microwave Irradiation

Abstract Under microwave irradiation on clay a series of transformations of a number of phenols into their aryloxyacetic acids 3 and then their methyl esters 4 and hydrazides 5 has been achieved efficiently in good yields.

Novel Regioselective Hydroxyl-Alkylation of 4,5-Diphenylimidazole-2-Thione and A Competitive Intramolecular Ring Closure of the S-Hydroxyalkyl-Imidazoles to Imidazo[2,1-b]Thiazines and Thiazoles. Role of Catalyst, Microwave Irradiation, and Solid Support

Under both conventional method (CM) and microwave (MW) irradiation (MWI) conditions, alkylation of 4,5-diphenylimidazole-2-thione (1) with halogeno-alkanols 2 or 5, chloroglycerol 11 and 2,3-O-isopropylidene-1-O-(p-tolylsulfonyl)-glycerol (8) in presence of sodium ethoxide or sodium acetate in alcohol afforded regioselectively the corresponding S-alkylated analogues 3, 6, 9, and 12; they also were obtained using MW in absence and presence of bentonite as solid support with no change in regioselectivity. In the presence of potassium carbonate in DMF, the bisalkylated analogues 4, 7, 10, and 13 were obtained except in case of compound 13 where it was accompanied with the imidazothiazine 14. A convenient approach for imidazo-[2,1-b]thiazines and thiazoles 14–16 could be achieved by intramolecular dehydrative ring closure of the S-hydroxyalkylated imidazoles 3, 6, and 12 using potassium carbonate in DMF under both conventional and microwave methods. Isopropylidenation of 12 and 13 and deprotection of 9 and 10 also were investigated.

Synthesis of 5‐Aryl‐3‐Glycosylthio‐4‐Phenyl‐4H‐1,2,4‐Triazoles and Their Acyclic Analogs Under Conventional and Microwave Conditions

Under microwave irradiation (MWI), 4‐phenyl‐5‐substituted‐4H‐1,2,4‐triazole‐3‐thiol derivatives 7 and 8 were synthesized in a good yield by intramolecular cyclization of the aroyl phenyl thiosemicarbazides 5 and 6. The respective triazolylglycosides (Str‐glycosides) 12–17 were obtained by reaction of triazoles 7 and 8 with glycosyl halides 9–11 in dry acetone in the presence of potassium carbonate as base under both conventional and MWI conditions. Alkylation of 7 and 8 with haloalchols 18–20 in boiling ethanolic solution containing sodium ethoxide as a base gave the corresponding alkylated analogs 21–26. MWI conditions led to higher yield in shorter reaction time than the conventional method. Treatment of 26 with tosyl chloride gave the unexpected product 29 and not 27 or 28. Oxidation of 26 with sodium metaperiodate afforded triazole 8 and not the aldehyde 30. Attempted glycosylation and alkylation of the phenolic OH group in triazole 8 were unsuccessful; this was proved by theoretical calculations using the AM1 semi‐empirical method.

Acyclo C-Nucleoside Analogs. Regioselective Annellation of a Triazole Ring to 5-Methyl-1,2,4-Triazino[5,6-b]Indole and Formation of Certain 3-Poly Hydroxyalkyl Derivatives

ABSTRACT Cyclodehydrogenation of the ethylidene derivative of (5-methyl-1,2,4-triazino[5,6-b]indol-3-yl)hydrazine (1) gave the angular isomer, 1,10-dimethyl-1,2,4-triazolo[3′,4′:3,4][1,2,4]triazino[5,6-b]indole (4). The linear isomer, 3,10-dimethyl-1,2,4-triazolo[4′,3′:2,3][1,2,4]triazino[5,6-b]indole (7) could be prepared regioselectively by the cyclodehydration of the acetyl derivative of 1. The cyclodehydrogenation was extended to the monosaccharide derivatives of 1. The role of the N-methyl group on the site of annellation has been discussed.

Microwave irradiation for enhancing the regioselective synthesis of 6H-indolo[2,3-b]quinoxalines

Microwave irradiation (MWI) promotes the regioselective synthesis of 6H-indolo[2,3-b] quin oxaline (5) by condensation of isatin (1) with o-phenylenediamine. Ethyl indolo [2,3-b] quinoxaline-6-acetate (8) was prepared via the carbethoxymethylation of 5, or from the reaction of N-(ethoxycarbonylmethyl)isatin (6) with o-phenylenediamine under MWI. The reaction of 8 with hydrazine hydrate afforded the hydrazide 9, whose condensation with aromatic aldehydes and monosaccharides gave the hydrazones 10a–d.

1H and 13C NMR Spectra of Alditolyl Derivatives of 3-Hydrazino-5-Methyl[1,2,4]triazino[5,6-b]indole and Their Cyclized Products.

Abstract The 1H and 13C NMR spectra of sugar (5-methyl [1, 2, 4]-triazino [5, 6-b] indol-3-yl) hydrazones (1), per-0-acetyl aldehydo sugar 1-acetyl-1-(5-methyl [1, 2, 4] triazino [5, 6-b]-indol-3-yl) hydrazones (2), l- (penta-0-acetyl-pentitol-1-yl)-10-methyl [l, 2, 4] triazolo [3′, 4′:3, 4] [l, 2, 4] triazino [5, 6-b]-indoles (3) have been investigated. The 2 D NMR (H, C COSY) spectrum of 2a has been studied.