New strategies for synthesis of partially fluorinated heterocycles as precursors for trifluoromethyl-substituted polymers

The building-block strategy is applied to the synthesis of new compounds with two five-membered heteroaromatic units. The heteroaromatic rings contain a fluorine atom which is activated towards nucleophilic displacement reactions by an adjacent trifluoromethyl group. The difunctional compounds can be converted into poly(arylene ether)s by base-catalyzed polycondensation with bisphenols or bisthiophenols. Trifluoromethylated poly(arylether oxazole)s and poly(arylthioether oxazole)s are obtained by this route. All representatives of these two new classes of polymers are soluble in common organic solvents. Reaction conditions for the polycondensation as well as thermal stability, glass transition temperatures, and molar masses of the polymers are described.     

Synthesis of trifluoromethyl-substituted cyclopropanes via sequential Kharasch-dehalogenation reactions

A two-step process for the synthesis of trifluoromethyl-substituted cyclopropanes is described. Halothane, an anesthetic agent, is added to olefins in a ruthenium-catalyzed Kharasch reaction. The resulting 1,3-dihalides are converted into cyclopropanes by dehalogenation with magnesium. This procedure represents an alternative to metal-catalyzed cyclopropanations involving trifluoromethyl diazomethane.     

Glycoconjugate libraries accessed by multicomponent reactions

Glycobiology opens a wide field for new therapeutic approaches. However, the complexity and unavailability of various carbohydrate test compounds has excluded this class of natural products from modern screening systems. Alternatively, glycomimetics are considered to be more drug-like candidates for development. By means of multicomponent condensations (MCCs) utilizing suitable carbohydrate synthons, rapid and effective access to glycoconjugate libraries can be obtained. The flexibility of MCCs allows the assembly of diverse carbohydrate containing libraries. It may be assumed that MCCs containing carbohydrate moieties will play an important role in glycomimetic chemistry and biology.     

Recyclization reactions of heterocycles

The direction of recyclization during hydrazination of isoquinolinium salts is practically independent of the substituent attached to nitrogen and the reaction conditions and leads to compounds with an N-aminoisoquinoline structure.See [1] for communication XIV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 961–965, July, 1974.     

Recyclization reactions of heterocycles

2,5-Dimethyl-1,3,4-oxa- and -1,3,4-thiadiazoles are recyclized to 2,5-dimethyl-4-amino-1,2,4-triazole on reaction with hydrazine. Recyclization occurs with greater difficulty and only with oxadiazole in the case of alkylhydrazines. Nitration of 2,5-dimethyl-4-amino-1,2,4-triazole gives its N-nitroamino derivative.See [1] for communication XVIII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 853–855, June, 1976.     

Recyclization reactions of heterocycles

2-Thioxo-4-oxazolidone and thiazolidines containing heteroatom substituants (O, S, and NH) in the 2 and 4 positions are converted to benzimidazole derivatives on reaction with o-phenylenediamine. The direction of these recyclizations depends on the nature of the heteroatom substituents in the 2 and 4 positions of the heteroring.See [1] for communication XX.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 666–668, May, 1978.     

Tetrachlorosilane catalyzed multicomponent one-step fusion of biopertinent pyrimidine heterocycles

Multicomponent one-step fusion of a variety of pharmacologically pertinent pyrimidine heterocycles has efficiently been achieved from their respective aldehydes, β-dicarbonyl compounds, and urea/thiourea in the presence of a catalytic amount of tetrachlorosilane in DMF/AN mixture at normal ambient temperature.     

Natural products as templates for bioactive compound libraries. 3*. novel heterocycles and peptidomimetics generated from anabasine by isocyanide-based multicomponent reactions

Anabasine served as a starting material for the synthesis of two series of novel, drug-like compounds. On the one hand, anabasine was subjected to a direct Chichibabin amination and elaborated into medicinally relevant, racemic 6-(piperidin-2-yl)imidazo[1,2-a]pyridines via the Groebke–Blackburn reaction. On the other hand, anabasine was used as an amine for the Ugi reaction to provide novel non-racemic anabasine-containing 2-[(2-pyridin-3-yl)piperidin-1-yl]acetamide peptidomimetics with high diastereoselectivity.     

Phototransposition reactions of methyl-substituted benzotrifluorides: proof of the role of trifluoromethyl-substituted carbon

Irradiation in acetonitrile of any one of the six isomers of dimethylbenzotrifluoride 8 resulted in efficient photoisomerization to the others. The dominant processes in these phototransposition reactions divides the isomers into two triads. The first consists of 8-2,6 (2,6-dimethylbenzotrifluoride), 8-2,3, and 8-3,4; the second consists of 8-3,5, 8-2,4, and 8-2,5. Moreover, irradiation of 2,6-dideuterio-4-methylbenzotrifluoride 5-d(2) resulted in formation of 5,6-dideuterio-3-methylbenzotrifluoride 6-d(2). These observations demonstrate that it is the trifluoromethyl-substituted carbon that is the migratory one in these reactions.     

Construction of multifunctional heterocycles bearing aza-quaternary carbons by titanocene-catalyzed umpolung reactions

The combined application of Grignard/Reformatsky addition and the titanocene-catalyzed umpolung α-amino carbon-carbon bond formations provided a flexible and versatile protocol for preparation of multifunctional pyrrolidinones/piperidinones/N-Boc-piperidines bearing aza-quaternary carbons (AQC) from cyclic imides and analogues. Based on these multifunctional single-ring motifs, several advanced AQC-bearing heterocycles, such as AQC-possessing indolizidines and 1-azaspirocycles, have been constructed efficiently.     

New heterocycles with cycloamidine substructure and their ringtransformation reactions with acetylene dicarboxylic ester

The synthesis of pyrido[2,1‐c]‐1,2,4‐triazines 6 , pyrido[1,2‐b]‐1,2,4‐triazines 7 and pyrido[1,2‐b]pyri‐dazines 8 respectively by cycloacylation of derivatives of pyridine with imidoylchlorides of type 2 is described. The heterocycles of type 6 as well as of type 7 can be ring‐transformed with dimethyl acetylenedicarboxylate. In contrast to pyrido[1,2‐a]pyrazines 1, a complex reaction including cleavage of the acetylene subunit takes place. Starting from compound 6a , the pyrrolo[2,3‐d]imidazole 11a could be isolated from a mixture of unidentified by‐products, whereas derivatives 7 gave nearly quantitatively the tricyclic products of type 12 .     

Recent developments in asymmetric multicomponent reactions

Multicomponent reactions (MCRs) receive increasing attention because they address both diversity and complexity in organic synthesis. Thus, in principle diverse sets of relatively complex structures can be generated from simple starting materials in a single reaction step. The ever increasing need for optically pure compounds for pharmaceutical and agricultural applications as well as for catalysis promotes the development of asymmetric multicomponent reactions. In recent years, asymmetric multicomponent reactions have been applied to the total synthesis of various enantiopure natural products and commercial drugs, reducing the number of required reaction steps significantly. Although many developments in diastereoselective MCRs have been reported, the field of catalytic enantioselective MCRs has just started to blossom. This critical review describes developments in both diastereoselective and catalytic enantioselective multicomponent reactions since 2004. Significantly broadened scopes, new techniques, more environmentally benign methods and entirely novel MCRs reflect the increasingly inventive paths that synthetic chemist follow in this field. Until recently, enantioselective transition metal-catalyzed MCRs represented the majority of catalytic enantioselective MCRs. However, metal contamination is highly undesirable for drug synthesis. The emergence of organocatalysis greatly influences the quest for new asymmetric MCRs.     

Synthesis of 4-keto pimelates by palladium-catalyzed carbonylativesymmetrical coupling of siloxycyclopropanes

Treatment of 1-alkoxy-1-siloxycyclopropane with a catalytic amount of a palladium/phosphine complex in chloroform under carbonmonoxide atmosphere gives 4-keto pimelate.     

A facile and efficient synthesis of enyne-reaction precursors by multicomponent reactions

Using improved reaction protocols for three-component coupling reactions of aldehydes, dienophiles, and amides (AAD-reaction) or anhydrides (ANAD-reaction) or orthoesters (ALAD-reaction), a variety of functionalized hexahydroisoindolo derivatives were synthesized and fully characterized. Condensation of ubiquitous available aldehydes with unsaturated amides or anhydrides or orthoesters and subsequent Diels-Alder reactions with electron deficient dienophiles furnishes endo-selective enyne-reaction precursors in good to excellent yield.