Abd El-Wareth A. O. Sarhan

A convenient one-pot synthesis of 2-benzimidazolyl-thioacetophenones and thiazolo[3,2-a]benzimidazoles

Abstract 2-Mercaptobenzimidazole ( 1 ) reacts with aromatic ketones 2a-d in acidified acetic acid giving 2-benzimidazolylthioacetophenones 3a-d . Which on cyclization yield thiazolo[3,2-a]-benzimidazoles 4a-d . Acetylation of 3a,d gave the N-acetyl derivatives 5a,d . Cyclization of 3a-d or 5d in acetic anhydride or acetic anhydride / pyridine mixture afforded 6a-d . While reaction of 1 with aliphatic or alicyclic ketones gave directly 2,3-disubstituted thiazolo[3,2-a]benzimidazoles 7a-f and 8a-d respectively.

Utility and Synthetic Uses of Mannich Reaction: An Efficient Route for Synthesis of Thiadiazino‐[1,3,5][3,2‐a]benzimidazoles

Abstract The utilities of the Mannich reaction in synthetic organic chemistry are reviewed. The behaviors of Mannich reactions on several bifunctional heterocyclic compounds have been reported. A new class of heterocyclic compounds, thiadiazino[1,3,5][3,2‐a]benzimidazoles 12a–g, were obtained by reaction of 2‐mercaptobenzimidazole with primary aliphatic amines in a one‐step synthesis. An attempt to apply this reaction using primary aromatic amines lead to the formation of the well‐known Mannich bases 11a–g rather than the N‐substituted thiadiazines 13.

Chemoselective Reactions of 2,3-Dichloro-1,4-naphthoquinone

Summary. The reaction of 2,3-dichloro-1,4-naphthoquinone with alkoxides, primary amines, and phenols was shown to proceed chemoselectively rather to the corresponding 2-substituted 3-chloro-naphthoquinones or 2,3-disubstituted quinones than to brazanquinone derivatives. Difunctional reagents like mercaptobenzimidazole, methyl urea, or guanidine lead to the corresponding heterocyclic system. The chemoselectivity of these reactions was found to be critically dependent on the reagents and reaction conditions used. These reaction parameters can thus be used to govern the synthesis of distinct compounds.Zusammenfassung. Es wurde gezeigt, daß die Reaktion von 2,3-Dichlor-1,4-naphtho-chinon mit Alkoxiden, primären Aminen und Phenolen chemoselektiv zu den entsprechenden 2-substituierten 3-Chlornaphthochinonen und nicht zu Brazanchinonen führt. Der Einsatz von difunktionellen Reagentien wie Mercaptobenzimidazol, Methylharnstoff und Guanidin ergab die entsprechenden tricyclischen heterocyclischen Systeme. Es wurde gefunden, daß die Chemoselektivität dieser Reaktionen kritisch von den Reagentien und Reaktionsbedingungen abhängt. Diese Reaktionsparameter können verwendet werden, um die Synthese bestimmter Verbindungen zu steuern.

Synthesis, characterization and reactions of 2-deoxo-5-deazaalloxazines

5-Deazaflavins and their homologues have been known as potential riboflavin antagonists, bioreductives, and compounds with potent antitumor activity. 2-Amino-4-methylquinoline-3-carbonitrile (2) was prepared as unreported starting material for several interesting 2-deoxo-5-deazalloxazine derivatives. Cyclization of 2 using formamide afforded the 2,4-deoxo-5-deazaalloxazine derivative 7, which was subjected to deamination with nitrous acid to give the 2-deoxo-5-deazaalloxazine (8). The compound 8 was also obtained via 13 by treating the latter with refluxing formic acid or formamide and used as a precursor for synthesis of several 2-deoxo-5-deazaalloxazines 18, 19, 20, 21 and 22. The pharmacological and biological properties of these compounds are still under investigation.

On acidification of thiols to produce the corresponding disulfides

Thiophenol 1, 2-mercaptobenzimidazole (3a), 4,5-diphenylimidazole-2-thione 3b, and 5-mercapto-2-aryl-1,2,4-s-triazoles (6a–b) are chemically oxidized using the acidified acetic acid method to the corresponding disulfides 2, 5a–b and 7a–b, respectively. The structures of the disulfides thus formed were established both chemically and by spectral analysis.

A Convenient One-Pot Synthesis of Pyrazolo[3,4-d]pyrimidines and s-Triazolo[3,4-b][1,3,5]thiadiazines

Abstract The reaction of 5-amino-3-aryl-1-phenylpyrazoles (1a-d) with formaldehyde and secondary amines in boiling ethanol gave the corresponding 4-alkylaminomethyl derivatives (2a-f) and bis-(4-pyrazolyl)methane (4a,b) as byproduct. Such reaction with primary aliphatic and aro matic amines at room temperature afforded 1,3,5-trisubstituted (5a-h) and 1,3.5,7-tetrasubstituted tetrahydropyrazolo[3,4-d]pyrimidines (8a-k) respectively in good yield. Similarily, the Mannich reaction of 5-mercapto-3-phenyl-1,2,4-triazole (9) with secondary amines, in boiling ethanol, and primary aromatic amines, at room temperature, gave 2 -substituted aminomethyl derivatives (10a-c) and (14a-g) respectively,while with primary aliphatic amines, p-toluidine and p-anisidine,at room temperature,and with other primary aromatic amines, in boiling ethanol, afforded the cyclized products 12,4-triazolo[3,4-b]thiadiazines (13a-e); (15f,g) and (15a-e), respectively.

On the Synthesis of Dibenzohomobarrelenes

Abstract An efficient method for synthesis of the dibenzohomobarrelene compounds using a one-pot reaction is described. Reductive debromination-elimination of the mono- or di-bromo cycloadducts using Zn-Cu couple afforded the corresponding dibenzohomobarrelenes in various yields.

Cycloadditions of Metal Oxyallyl Cations Generated from αα′-Dibromoketones to Furan and Pyrrole

Summary. Furan (1) and 2,5-dimethylfuran (2) were added to tetrabromoacetone (4), 2,4-dibromopentan-3-one (5), and tribrombutanones 6a,b under different reaction conditions to give the corresponding cycloadducts 7–10, 11a,b, and 12a,b in moderate yields. Reductive debromination of 12a,b with Zn/CuCl/NH4Cl in methanol gave the debrominated cycloadduct 13 in good yield. The α,α′-dibromoketone 5 was added to 1-(2′-acetoxyethyl)pyrrole (3) to yield the corresponding cycloadduct 14 using the Na/Cu method. Upon attempted cycloaddition of 5 to the pyrrole derivative 3 using the (EtO)3B/Zn method, the 2-substituted pyrrole derivatives 15a–d were obtained. Almost all reactions resulted in the formation of a single isomer which by molecular mechanics calculations (MM3) also appeared to be the energetically most favored one.Zusammenfassung. Furan (1) und 2,5-Dimethylfuran (2) wurden unter verschiedenen Reaktionsbedingungen an Tetrabromaceton (4), 2,4-Dibrompentan-3-on (5) und die Tribrombutanone 6a,b addiert. Es entstehen die entsprechenden Cycloaddukte 7–10, 11a,b und 12a,b in bescheidenen Ausbeuten. Reduktive Debromierung von 12a,b mit Zn/CuCl/NH4Cl in Methanol führt in guter Ausbeute zum debromierten Cycloaddukt 13. Das α,α′-Dibromketon 5 konnte mittels der Na/Cu-Methode mit 1-(2′-Acetoxyethyl)-pyrrol (3) zum entsprechenden Addukt 14 umgesetzt werden. Der Versuch, diese Cycloaddition mit der (EtO3)B/Zn-Methode durchzuführen, resultierte in den 2-substituierten Pyrrolderivaten 15a–d. Fast alle Reaktionen ergaben einheitliche Produkte, die sich nach molekülmechanischen Berechnungen (MM3) als die energetisch günstigsten herausstellten.

[4+3]Cycloaddition Reactions: Synthesis of 9,10-Dimethoxy-9,10-propanoanthracen-12-ones

Cycloaddition of 9,10-dimethoxyanthracene (1) to tetrabromoacetone (2a) under a variety of conditions afforded isomers 3a,b; reductive debromination of 3a,b afforded 4, while reduction with NaBH4 gave alcohol 6 which on reductive debromination gave olefin 7; reaction of 1 with 2b gave isomers 8a,b.